ECMWF is currently developing a ground breaking non-hydrostatic atmospheric dynamics Finite Volume Module (FVM) which will be implemented in the ECMWF’s Integrated Forecasting System (IFS). The IFS is the operational tool used to provide medium range weather prediction services for the UK and most EU countries.

Many aspects of the spatial discretisation employed in the FVM originated from Dr Szmelter’s earlier work on unstructured mesh models for fluid flows. In recent years, these have been substantially advanced by ECMWF to take advantage of the IFS environment and High Performance Computing.

The main goal of the SRV is to discuss and initiate the implementation of an alternative discretisation of selected operators, which could potentially offer further improvements to the module in terms of accuracy and speed. Suitable numerical tests will be defined and set up. Dr Szmelter will also explore whether some of the advancements achieved for atmospheric flows in the FVM could be applied to other engineering and environmental flows.

Nematic liquid crystals (NLCs) are complex non-Newtonian fluids – anisotropic fluids with a degree of long-range orientational ordering. A rapidly growing research theme concerns “nematic microfluidics” or the flow of NLCs confined to thin channels. Experimentalists are keen to exploit nematic microfluidics for new applications in hydrodynamics, transport phenomena and next-generation pharmaceutical applications such as drug delivery.

The introduction of nanoparticles into NLCs modifies the fluid properties, and understanding this effect may lead to new applications. Some earlier collaborative work between Drs Majumdar and Griffiths on the flow of nanoparticles in nematic microfluidics showed interesting effects, especially in cases with multiple nanoparticles.

The SRV will therefore focus primarily on the flow of nanoparticles in nematic microfluidics, and through a combination of modelling, simulation and experiments, will address issues such as:

• how the nanoparticles interact with the fluid flow and the nematic orientation, and vice-versa;
• how this interaction can be manipulated to produce desired agglomerates with desired properties;
• how the shape and size of nanoparticles can be varied to manipulate the rheology;
• assessing the predictions of different mathematical theories for nematodynamics and how they compare to experiments.

The SRV will initiate proof-of-concept collaborative work to develop phononic structures (Glasgow) on thin-film ZnO surface acoustic wave devices (Northumbria). This has the potential of creating ultra-low-cost acoustofluidics devices, capable of carrying out complex microfluidic processing of samples for applications in flexible and wearable healthcare monitoring. Dr Fu will fabricate and test different designs of acoustofluidic device.

Prior to the SRV, suitable ZnO-coated substrate samples will be prepared at Northumbria, while Glasgow will carry out calculations to confirm the microstructure geometry to be used. Then:

• In the James Watt Nanofabrication Centre at Glasgow, different phononic structures (pillars or holes) will be patterned and fabricated on the ZnO-film-coated substrates
• The ultrasonic surface vibration patterns will be validated using a high-frequency laser Doppler vibrometer (frequency range in the 10’s of MHz)
• The microfluidic performance of fabricated devices will be tested using (i) conventional microfluidic test beds to look at streaming, flowing, jetting and nebulisation; and (ii) a high-frame-rate camera (up to 1MHz)

Following the SRV, the data will be used in support of new collaborative research bids, and in discussions with interested industrial partners who could develop microfluidics products for healthcare applications.

Dr Buxton has obtained three-dimensional experimental data on the behaviour of various turbulent flows (boundary layers, wakes, shear layers). With 3D data, the full velocity gradient tensor is available for analysis, and we will apply various vortex identification schemes to extract flow structure information. However, most of these methods are eigenvalue-based, so we will also derive complementary methods that incorporate effects excluded from consideration in an eigenvalue-based approach. Hence, we will be able to identify structures that are clear in both types of approach, as well as those that are better represented in one than the other. We will then seek to explain these differences in terms of local energy production and dissipation. Such analyses will inform the physical basis for future turbulence closures.

Several authors have reported anomalous blood flow patterns in tumour vasculature, including deviations from the typical haematocrit (red blood cell count) distributions observed in healthy tissue. Such abnormalities present a challenge for drug delivery and have been linked to tumour hypoxia and angiogenesis.

To date, most computational models of tumour blood flow view the blood as a homogeneous fluid and employ phenomenological rules to determine haematocrit changes at vessel bifurcations. Such models fail to capture the dynamics encountered in tumours. This is, in part, due to the computational challenges associated with simulating haematocrit changes in a mechanistic way, i.e. using a model of interacting deformable particles to describe the transport of red blood cells (RBCs) in the plasma.

The SRV will initiate a collaboration between the groups of Prof Byrne and Dr Bernabeu to exploit their complementary expertise:

• Prof Byrne and colleagues have considerable experience of simulating blood flow and oxygen distribution in tumours and have recently developed a microfluidics assay that recapitulates RBC dynamics in tumour vascular networks.
• Dr Bernabeu and colleagues have recently extended HemeLB, their blood flow simulation platform that treats blood as a suspension of red blood cells (http://www.archer.ac.uk/community/eCSE/eCSE01-010/eCSE01-010.php).

The SRV will focus on constructing and validating computational models of blood flow in realistic tumour microvasculature, based on experimental data recently obtained by Prof Byrne and colleagues. These models will be used to develop a mechanistic model of haematocrit changes.

Soap films are thin interfaces containing fluid and (stabilising) surfactant molecules. Not only is predicting the flow within them difficult, but predicting how they move is also technically challenging, yet it is significant in industrial applications such as oil recovery, medical products, and soil remediation.

The viscous froth model (VFM), which balances film curvature and adjacent bubble pressures with the friction experienced by the film, has been used to predict the foam flow in constricted narrow channel. However, it suffers from the simplifying assumption of constant surface tension along the film.

Gradients of surface tension develop along expanding/contracting films during flow, altering the force balance and changing foam flow rate and film stability. The Strathclyde group is currently developing surfactant transport models that will be included in the VFM.

The SRV will allow Dr Vitasari to discuss with Dr Grassia and Mr Rosario the implementation of their model in the VFM and hence to assess the effect of surfactant movement on foam flow and film stability, leading to joint journal publications and contribution to foam oil recovery process designs.

Traditionally, only the bed shear is considered as the driving force for sediment transport. Very little research has been reported concerning the influence of both the shear stress at the soil/water interface and the hydraulic gradient within the soil layer on the sediment motion.

The visit will focus on research to develop a novel sediment transport model using a Lagrangian computational technique. A dynamically-integrated free-surface and subsurface flow model will be developed using the SPH (Smoothed Particle Hydrodynamics) method, which will enable the inclusion of the contributions of both the bed shear stress and the seepage force to sediment transport. The developed model will be used to model the flow and scour around offshore pipelines to demonstrate its superiority over existing scour modelling techniques.

Silo honking is the harmonic sound generated by the discharge of a silo filled with a granular material. Previous work by Dr Vriend’s research group focused on the characterization of sound with high-fidelity microphones and capturing high-speed imagery of the moving particles through the side walls. The motion of particles touching the side walls, where the highest friction occurs, shows a fascinating pattern in space and time, but the behaviour of internal grains remains a mystery due to their inaccessibility for imaging.

The PEPT facility allows the real-time tracking of a radioactive tracer particle inside a sand-filled tube 2m long, with a 30x30cm section, at sub-millimetre spatial resolution and millisecond-scale temporal resolution. The particle is labelled in such a manner that is remains physically identical to all others within the system, making PEPT an entirely non-intrusive and non-destructive technique.

As PEPT imaging utilises high-energy (511 keV) gamma-rays, single-particle motion can be observed even deep within the bulk of large, dense and opaque systems, with a temporal resolution that cannot be achieved using more conventional tomographic techniques.

By repeating the experiment at different heights and positions in the tube, it is possible to extract full three-dimensional flow fields, in addition to numerous other single-particle and whole-field quantities, thereby providing critical and novel information for modelling silo honking.

Evidence has been collected on the existence of large-scale secondary motions in turbulent boundary layer developing over disparate roughness types. These Secondary Flows (SFs) modulate the mean flow, generating high- and low-momentum pathways, which in turn contribute to sediment transport, drag and heat transfer. Despite the importance and relevance of SFs in a variety of natural environments and engineering applications, their nature and genesis remain largely unclear.

This short research visit will focus on carrying out a series of controlled experiments to shed light on the physics of the generation of secondary motions in turbulent boundary layers developing over different rough topologies. This fundamental project aims at paving the way toward a deeper understanding of rough-wall physics. 3D Stereoscopic Particle Image Velocimetry data will be acquired on novel highly rough surfaces, which will include: (i) regular longitudinal roughness strips of 'infinitesimal' width and (ii) alternating spanwise strips of smooth and rough surfaces.

Chemical Vapour Deposition is a micro-fabrication process for growing epitaxial films a very few atoms thick. A reactant gas is pumped into a high temperature environment that fractures it into its constituent atoms and deposits them along a substrate. Limited prior work has been done that models the gas in a rotating-pedestal reactor as a modification to von Kármán flow. There is growing interest in whether the transitional boundary-layer flows present could hinder film growth; however, a comprehensive model has not yet been developed.

The applicant’s research aims to use modern stability techniques to develop a model of strong interest to the CVD community, and the SRV will make links with the CVD community and explore the limitations of the previous models by:

• Forging meaningful links with CVD researchers at MMU and discuss in depth different reactor designs and operations
• Identifying current fluid issues within CVD and how they might be modelled
• Further developing links with Dr Hussain and Prof Gajjar, authors of prior stability analyses of direct relevance
• Presenting analytical work to date to a non-fluids community

Surfactant mass transfer mechanisms in foam films, in the context of foam fractionation, include convective Marangoni flows along film surfaces that occur when foam films expand or shrink while moving through a channel, coupled with film drainage effects and mobile interfaces, changing the surfactant concentration on the interfaces and thus their surface tension. The associated film deformations have a direct impact on the viscous froth model, being developed by the Aberystwyth group, and so need to be considered to produce a more realistic model for foam flows.

This SRV represents an excellent networking opportunity and a chance to understand how the applicant’s current work on surfactant mass transfer mechanisms can be adapted to the deforming foam films studied by Prof Cox’s group. The SRV will also facilitate knowledge exchange between the foam modelling groups in the University of Strathclyde and Aberystwyth University, focusing on the inclusion of surfactant mass transfer mechanisms on bubble interfaces, to estimate better the film surface tension used in the viscous froth model of foams flowing in microfluidic channels.

This project can have great impact in a wide range of industries using foams in microfluidic channels, including medical, pharmaceutical, biological and oil recovery fields, as well as contaminated soil remediation.

The SRV will form part of an investigation into the process of eye formation in vortex structures - the development of a region of weak reversed flow in the vicinity of the central axis of the vortex. One aim of this work is to improve the fundamental understanding of the key dynamical processes that may occur in atmospheric vortices which are at present poorly understood. A model problem based on rotating convection in a cylindrical domain is being used to examine these processes.

Analytical work and numerical simulations have already been carried out, but it is intended to perform laboratory experiments to demonstrate the theory and complete the project. Such experiments require a suitable rotating table and tank: these will be provided by the AOPP laboratory at the University of Oxford, who will collaborate on the experimental programme. The flow will be visualised in different regimes through the use of dye, and velocity measurements will be made using particle tracking where possible.

A key challenge in any experimental study of decontamination and cleaning is to identify a suitable model contaminant for the problem at hand. This is particularly true for chemical decontamination research, where studies using real contaminants are prohibitively dangerous.

The Hazard Management Team at dstl recently synthesised a novel ionic liquid dye. It is a red, viscous liquid which fluoresces when dissolved in water. Its physical properties are therefore similar to important chemical weapon systems and other common soils (e.g. custard), while its optical properties enable experimental techniques such as dye attenuation to be used. The dye also has great potential for other fluids applications, such as studies involving mixing or dissolution in geological contexts.

The SRV has two primary aims: (i) learning how to synthesise the dye, so that this knowledge can be transferred to DAMTP, making the dye available for fluid dynamics experiments there; and (ii) exploring the use of this dye to model experimentally droplet decontamination in small gaps by using it in a laboratory-scale decontamination setup, to be transported to dstl for the purpose.

This research will be a continuation of a long and successful collaboration between DAMTP and dstl, which has already led to some important technology transfers in both directions, and will develop further close ties between academic and government scientists.

Multiphase flows where two or more fluids have interfacial surfaces are often found in industrial engineering applications. Despite the fact there are a number of numerical studies on two-phase flows, research on three-phase flows (gas-liquid-liquid) is still limited.

The SRV will focus on the development of numerical methods for three-phase flows and both interface tracking and interface capturing approaches will be explored. This SRV will also facilitate collaboration between Dr Xie and Dr Li and his research group on various multiphase flows problems, such as bubbles, droplets and jets.

The SRV will advance a project to set up lattice Boltzmann simulations of SLIPS, surfaces coated with a thin layer of lubricant that have very low contact angle hysteresis, in order to understand the dynamics of droplets moving across these surfaces.

The mobility of the lubricating film greatly reduces the (lateral) adhesion, so that deposited liquid or solid particles, bacteria or other microorganisms can slide off easily as soon as the surface is tilted by a few degrees. This would make it useful for industrial applications, e.g. easy-to-clean surfaces, anti-icing or anti-biofouling. To develop durable and environmentally friendly SLIPS interfaces, understanding of the interplay and physical interactions between the solid surface topography, the lubricating film and the liquid under static and flow conditions is necessary.

It has become clear that a recent three-phase lattice code developed by Dr Kusumaatmaja would be ideal for the project and so the SRV will allow collaboration between Oxford and Durham both on extending the code and on applying it to physical systems.

Liquid jets and sprays are commonly used to clean equipment in pharmaceutical manufacturing between successive batches of the same product or different products. The applicant’s work has so far been focused on static jets impinging on a soiled surface, while the Cambridge group has also been looking at dynamic jets, and has a test rig set up to study this. The applicant will conduct tests on the Cambridge rig with the same soils used in his earlier static jet tests, to compare the removal mechanisms and energy efficiency of static vs. dynamic jets.

The SRV will also look at spray cleaning. Sprays tend to leave a very thin residual film when there is no surfactant present, and a method is needed to quantify the cleanliness of the surface after cleaning. Prof Wilson has access to a confocal thickness sensor system, manufactured by Micro-Epsilon, which measures thin residual films on a surface after it has been cleaned. This sensor will therefore be ideal for quantifying the effectiveness of spray cleaning. In turn, the use of spray nozzles in the Cambridge rig will be of potential use and interest to the group, since to date they have not investigated spray cleaning in detail.

Due to the difficulty of solving Euler's equations in three dimensions, meteorologists and mathematicians have sought approximations to this system in the case of the atmosphere and oceans. The semi-geostrophic model is such an approximation, of particular mathematical interest due to its close connection with convex functions and the fully nonlinear Monge-Ampere equation. In terms of the atmosphere, these equations neatly encapsulate the formation and movement of weather fronts, or describe orographic separation (flow over a mountain). 

However, much work is needed in terms of connecting the physical to the mathematical, and this project aims to show that the semi-geostrophic model is indeed a valid approximation of the Euler equations in the case of atmospheric flows.

While the applicant's PhD project focuses on the rigorous analysis of asymptotic limits of the Euler and semi-geostrophic equations, the motivation for the research is driven largely from the quest to improve numerical weather prediction models.

The applicant will visit Dr Mike Cullen, a long-standing expert in this field, to discuss setting the work in context, as well as taking the opportunity to discuss semi-geostrophic dynamics with others working in this area at the Met Office. 

Dr Canyelles Pericas is engaged in a KTP collaboration between Epigem and Northumbria University, which has developed a SAW platform for biological assays. The KTP team has the requisite knowledge in thin films, manufacturing, microfluidics and electronics, but requires further expertise in biological assays and the acoustofluidics processes involved in performing them.

Dr Canyelles Pericas will work with Dr Reboud and Dr Wilson at the University of Glasgow, who have pioneered the technique on single crystal wafers. During the visit, Dr Canyelles Pericas will bring the Epigem-Northumbria platform to Glasgow, where assays will be performed using spiked mock samples (DNA in buffers) in the first instance, benchmarked against gold standard techniques available in the Glasgow laboratories (real-time PCR system used in clinics and testing laboratories in hospitals). If successful, more complex samples, such as blood or milk, or a mixture of different markers, will be spiked together to explore multiplexed detection.

The SRV will provide Epigem-Northumbria University with an understanding of the biological assay processes; University of Glasgow will benefit from exposure to thin film capabilities, which would be of benefit to their work by helping to decrease the costs of many methods.

Overall, the visit will result in a novel platform to perform DNA-based tests on flexible substrates for point-of-care diagnostic applications. It will also cement future collaborations between all three partners seeking funding from InnovateUK and Horizon 2020.

The aim of the SRV is to use flow control techniques to significantly reduce jet noise and aerofoil noise. In particular, experimental research will be carried out to reduce jet noise installation effects through active and passive flow control techniques.

The University of Bristol is home to a state-of-the-art aeroacoustics research facility, which has specific features to perform cutting-edge research on jet noise and aerofoil noise.

The SRV will enable Cranfield and Bristol to strengthen their research collaboration in this field and is expected to result in a number of joint research proposals in the field of jet noise, aerofoil noise and flow control techniques for noise reduction.

The SRV will be used to conduct a collaborative experiment with Dr Park at the University of Dundee in their novel oscillatory flow tunnel. This facility is unique, in that it can generate orbital velocities up to 2 m/s, which are typical velocities for near-bed oscillatory flows generated by large storm-condition waves in the coastal zone. Under such conditions bed forms are washed out and sediments are transported in a thin high-concentration layer called the sheet flow layer.

In this experiment, PIV measurements will be made above and (partially) within the sheet flow layer using a high-speed camera and laser sheet generated by a continuous (Ar-Ion) laser source. To facilitate optical access into the sheet flow layer, transparent spherical glass beads (100-200 µm diameter) will be used to mimic sand particles.

The measurements will give novel insights into boundary layer and sheet flow layer dynamics under oscillatory flow conditions, and it is expected the visit will serve as a stepping stone towards a joint EPSRC proposal on sediment transport process under high-energy wave conditions

Surface nanobubbles can induce slippage at liquid-solid surfaces (D. Lohse & X. Zhang, Rev. Mod. Phys. 87, 981-1035, 2015). Different theoretical models have been proposed to reconcile the slip predictions with experiments; however, none so far have considered gas rarefaction effects.

The applicant recently used molecular dynamics (MD) to demonstrate the importance of gas rarefaction effect on slip over nanofilms (S.B. Ramisetti et al. Phys. Rev. Fluids 2(8), 084003-1-15, 2017) and is currently applying it to surface nanobubble slip problems.

The proposed SRV will permit collaboration with Dr Botto to analyse gas rarefaction effects in these latest simulations. Specifically it would address i) the development of a new slip length model considering gas rarefaction effects inside the nanobubbles, and ii) how to interpret and compare MD slip length results with published experimental data.

The visit would also allow discussions with Dr Karabasov to learn about QMUL’s new hybrid NS-MD multiscale code and discuss possible use of it to run flow simulations of the nanobubble problem.

The outcomes of this visit are expected to lead to a joint publication in the near future.

Analysing the effect of impinging gas jets on liquid layers is not only of fundamental interest, but also presents great industrial importance, e.g. for metallurgical applications. The SRV will bring together the experimental and theoretical capabilities of the hosts at Loughborough University and the visitor to synergistically develop a comprehensive understanding of this process.

The physical problem involves the competition of numerous effects, including inertia, gravity, surface tension and viscosity. Despite several investigations, a systematic study over a wide range of parameters has not yet been performed. Also, most studies have focused on analysing the interface shape, whereas studying flow patterns inside the liquid is of equal importance, e.g. for understanding heat and mass transfer. Coupled with a rich behaviour in a large parameter landscape, the experimental observations performed on-site are to be complemented by the derivation of novel non-local reduced-order models. While simplified, these offer great insight into relevant regimes and timescales of the setup.

Bridging the experimental work and the analytical progress will be the implementation of a state-of-the-art DNS platform, running on high performance computing clusters, whose role will be two-fold: i) it will act as a validation mechanism and a tool to establish the range of validity of the reduced-order models and ii) in highly nonlinear regimes outside of the scope of the modelling work it is to act in conjunction with the experiments to offer insight into flow quantities which are difficult to measure and interpret.

This 3-way approach is anticipated to yield renewed and extensive insight into this challenging multi-phase flow, while making ideal use of the resources and expertise of each of the participants during the course of the SRV.

The visit will also provide and strengthen collaborative ties with Dr D. Tseluiko and the other members of the Mathematical Modelling and Nonlinear Waves groups (Dr D. Sibley, Prof R. Smith, Prof A. Archer, Dr K. Khusnutdinova, Dr G. El, Dr E. Renzi) on related multi-fluid problems involving liquid films and electrohydrodynamic control of small-scale liquid systems, which lie at the intersection of current research interests.

Scalable mesh- and Re-independent solvers are of core importance in the simulation of fluids. A very promising strategy for achieving this for the stationary incompressible Navier-Stokes equations is the augmented Lagrangian method of Benzi and Olshanskii (SIAM J. Sci. Comput. 28(6), 2095–2113, 2006).

The main goal of this visit is to develop a multigrid solver in the Firedrake finite element framework (www.firedrakeproject.org) based on the scheme of Benzi & Olshanskii (op. cit.). The SRV will extend the existing support for geometric multigrid, which Firedrake already provides for elliptic operators, to incorporate abilities to provide custom grid transfer operators. This is necessary to obtain Re-independence in the Benzi-Olshanskii scheme, where a correction equation is solved as part of the prolongation. In addition, the SRV will extend existing additive Schwarz patch smoothers to provide multiplicative updates.

This multigrid solver will then be incorporated into Wechsung’s work on shape optimisation via shape calculus, where the current limiting factor is the scalability of the underlying flow solver.

The resulting preconditioner will be documented and made available to the UK fluids community as part of the open source Firedrake software.

Combustion noise is classified into direct and indirect noise. Direct noise is produced by the unsteady heat release of the flame, while indirect noise is caused by the acceleration of temperature and compositional inhomogeneities. There are still questions which remain unanswered regarding the effects of dispersion on compositional inhomogeneities and hence indirect noise.

Experimental data have been obtained at Cambridge using the Cambridge Wave Generator (CWG). In this set-up, gases of different composition are injected radially into a mean flow of air to produce a compositional ‘wave’. Once accelerated through a nozzle, this wave produces indirect noise.

The LES code developed at Imperial (BOFFIN) can handle both the turbulent mixing and dispersion, as well as the compressible flow boundary conditions arising in the flow, allowing us to compare the output pressure and concentrations to the experimental results. The SRV will allow the applicant to visit Imperial College to learn how to use the code for the test cases.

The UK leads the way in commercializing tidal energy, with several large-scale Tidal Energy Convertors (TEC) installed and connected to the grid. These devices extract energy from the natural tidal streams, causing tidal stream decay and flow passage blockage. This issue raises a pressing question – how much energy extraction will change the general tidal circulation pattern? This change may shift the balance of sediment transport in the coastal area and endanger the coastal public safety. In addition, the change of tidal stream distribution can compromise the productivity of existing and planned tidal energy plants.

The proposed collaborative study between Heriot-Watt University and University of Dundee will focus on the area around the Orkney Islands, which is one of the top marine energy development centres in the world. The tidal circulation system around these islands features a strong tidal stream in the Pentland Firth, which is a narrow strait connecting the North Atlantic Ocean and the North Sea. The prosperity of the local commercial marine energy business relies on this unique high-speed stream. However, there is a concern that the blockage effect and the energy harnessing process in Pentland Firth may alter the general flow pattern and compromise the business outlook.

The proposed SRV is targeted at connecting the local researchers to collect existing onsite datasets and develop a reliable numerical model. A sensitivity study will be conducted using the numerical model to discover if there is a critical threshold beyond which flow and sedimentation around the Orkney Islands changes abruptly.

The proposed SRV will develop responsive gel-based smart soft structures with enabled functions and enhanced flexibilities, which hold a great potential to advance current technologies in bio-medical device fabrication, i.e. intraocular lens. The SRV will combine the experience of Northumbria in materials and mechanics with the expertise of Heriot-Watt University (HWU) in micro- and nano-fabrication.

The core experiment will use Focused Ion Beam (FIB) machined diamond cutting tools to fabricate nanostructures on a soft matter surface and observe the surface interaction between the gel structure and an ionic liquid. The fabrication will take place at HWU's micro-/nano-manufacturing research lab (facilities include FIB Scanning Electron Microscope, Atomic Force Microscope, nanoindentation, etc.).

The preliminary outcomes anticipated from the SRV would be used in an EPSRC grant application, expected in April 2018, and further work is expected to result in a paper for submission by the autumn of 2018.

Direct Numerical Simulation and Large Eddy Simulation of high Reynolds number shear flows are now within reach of large-scale industrial application. The sensitivity of shear flows to their initial conditions has been noted for several categories of free shear flows, but an understanding of this sensitivity is currently lacking. Recent work by Dr McMullan has shown that the sensitivity of mixing layers to inflow conditions may be explained by the nature and magnitude of the fluctuations present in the upstream laminar boundary layer; his current research programme focuses on applying this knowledge to other shear flows, and on developing models to characterise the dependency of the flow evolution on its initial conditions.

This SRV aims to develop a framework to quantify the effects of inflow conditions on shear flows. Both canonical flows, and flows of practical engineering interest, are to be considered. Of specific interest in this SRV are:

• Establish meaningful collaboration with the group at Cardiff University.
• Analyse existing simulation data on rectangular circular cylinder flows, and backwards facing step flows, to understand the effect of inflow conditions of the flow.
• Develop a programme of research for future joint PhD students between Cardiff and Leicester.

This SRV will enhance connections between Cardiff and Leicester and promote interplay between the 'Rotating flows and complex boundary layers' and 'Turbulent Shear Flow' SIGs. It will also lead to collaborative research in the area of combusting shear flows.

The rotating disk boundary layer is considered an archetypal model for studying the stability of three-dimensional boundary-layer flows, as it is one of the few truly three dimensional configurations for which there exists an exact similarity solution of the Navier-Stokes equations. The crossflow inflexion point instability mechanism is common to both the rotating disk boundary layer and the flow over a swept wing, and thus the investigation of strategies for controlling disturbances developing in the rotating disk flow may prove to be helpful for the identification and assessment of technologies that have the potential to maintain laminar flow over swept wings.

The concept of developing novel drag reduction techniques by designing surface roughness has been well-studied, and this SRV aims to extend the recent work of Prof Garrett and colleagues. Using time-dependent simulations, it will study the effects of surface roughness on the impulse response, leading to an understanding of the effects on the absolute instability in the flow. The work undertaken during this SRV will also form a natural extension of methods developed during the applicant’s PhD, and some relatively simple modifications could prove to explain some of the stability characteristics shown by surface roughness, and have a great impact in this field.

This project will build on links developed through the SIG ‘Boundary layers and complex rotating flows’, and further enhance partnerships between the three research groups at Cardiff, Leicester and Warwick. The SRV will also develop international ties with KTH, Stockholm, as Dr Antonio Segalini will be present for the duration of the Leicester visit.

The aim of the proposed SRV is to enable Prof Wilson to spend a full working week in Bath working closely with Dr Trinh to revive their collaboration on fluid-structure interaction problems at small scales which was originally begun when they were both visiting Professor Howard Stone’s research group in 2011. That collaboration resulted in a paper on the analysis of viscous flow beneath a free or pinned rigid plate (P.H. Trinh et al. J. Fluid Mech. 760, 407-430, 2014); the SRV would extend this to the considerably more challenging problem of viscous flow beneath a pinned deformable elastic sheet.

(Semi-)implicit time-stepping methods can improve the speed of fluid dynamics simulations by avoiding prohibitively small time-steps. However, since those methods require the solution of a linear system at every time-step, it is still unclear if they are competitive with simpler time-explicit integrators. The development of competitive semi-implicit Discontinuous Galerkin (DG) methods has been complicated by the fact that they lead to linear systems which are hard to precondition.

Hybridized versions of the DG-method overcome this problem by introducing an equation for flux unknowns on the grid-facets [1,2]. The new SLATE language [3] allows the implementation of hybridized DG methods in Firedrake (https://www.firedrakeproject.org/), facilitating breakthroughs in the exploration of semi-implicit hybridized DG methods for realistic flow problems.

The visit of EM and JB will have the following objectives:

• knowledge transfer from experts in numerical fluid dynamics and hybridized DG methods
• collaboration with Firedrake developers to implement efficient multilevel preconditioners for hybridized DG methods, following [4]
• preparation of results for a talk at PDESoft 2018 and initial work on a joint publication

References

[1] Bui-Thanh, T., 2016. SIAM J. on Sci. Comp., 38(6), pp.A3696-A3719.

[2] Kang, S., Giraldo, F.X. and Bui-Thanh, T., 2017. arXiv:1711.02751.

[3] Gibson, T.H., Mitchell, L., Ham, D.A. and Cotter, C.J., 2018. arXiv:1802.00303

[4] Gopalakrishnan, J. and Tan, S., 2009. Num. Lin. Alg. with Appl., 16(9), pp.689-714.

The purpose of the visit is to collaborate on problems in electrohydrodynamic surface waves, in particular to extend the previous results [1] to a more general two-layered case.

The motivation of this work comes from physical and industrial applications, such as cooling systems in heat transfer and coating processes in the manufacture of a number of products. A good understanding in electrohydrodynamic surface waves can benefit the engineering community greatly due to the practical significance.

The problem is set up as follows. A perfectly conducting fluid is bounded above by a dielectric gas. Normal or tangential electric fields are imposed throughout the space. Previous work has been carried out, especially in the case where the depth of the fluid is assumed to be small in comparison to the wavelength. A number of model equations have been derived, e.g. the Korteweg-de Vries Benjamin-Ono equation. This was well summarised in [2]. However, to our knowledge, fully nonlinear time-dependent computations have not been performed so far.

We propose a valid numerical scheme based on the hodograph transformation which was first pioneered by Dynachenko et al. [3]. The two domains (fluid and air) are mapped differently and matched right on the interface by using an interpolation method. This allows us to compute steady solutions. For a time-dependent simulation, a fixed-point iteration method is employed at each time step to perform the interpolation.

Within such a framework, we aim to study the solution branches of fully nonlinear periodic waves, solitary waves and generalised solitary waves as well as their dynamics and stabilities.

References

[1] Gao, T., Milewski, P. A., Papageorgiou, D. T. & Vanden-Broeck, J.-M. 2017. Dynamics of fully nonlinear capillary-gravity solitary waves under normal electric fields, J. Eng. Math., 1-16.

[2] Wang, Z., 2017. Modelling nonlinear electrohydrodynamic surface waves over three-dimensional conducting fluids. Proc. R. Soc. A, 473, No. 2200, p. 20160817.

[3] Dyachenko, A. I., Kuznetsov, E. A., Spectorm, M. D. & Zakharov, V. E. 1996 Analytical description of the free surface dynamics of an ideal fluid (canonical formalism and conformal mapping). Phys. Let. A 221, 73-79.

There are significant challenges in the integration of microfluidics, for sampling, with biosensing, for detection, due to the different technologies that each function relies on. A critical issue is that the design of diagnostic devices based on current lab-on-chip approaches is limited by materials and fabrication processes designed around inherently rigid substrates (ceramic, Si or glass), unsuitable for flexible applications. Northumbria’s SAW devices provide multiple microfluidic functions including liquid mixing, transport, jetting and nebulisation, which will be integrated and used to mix target solutions and to pump the liquid to be detected to the sensing region of FBARs that have demonstrated clinically precise performance as biosensors. The visit will integrate efficient microfluidics using SAWs with precision sensing using FBARs onto one platform, by controlling the material properties using new manufacturing techniques.

Prior to the visit, RT will deposit thin films of ZnO on substrates (Al foil and polymer) and prepare flexible SAW devices, while the team in Cambridge will prepare FBARs to integrate with SAW devices for the lab-on-chip platform.

In Cambridge University, the team has access to a high frequency RF probe station and a sensing system based on a network analyser to obtain the frequency shift simultaneously for the biosensing applications. RT will measure the resonant frequency of all devices and will do some liquid fluidics sensing work in Cambridge.

The integrated devices will be transferred to Northumbria to continue microfluidic characterisation on standard test-beds. The resulting proof-of-concept data will be used in support of an EPSRC proposal, as well as in discussions with interested industrial partners (such as Epigem Ltd, a UK SME with interest in microfluidics products for healthcare applications).

It is well known that injection of a Newtonian fluid into a boundary layer acts to alter the characteristics of the flow significantly. This injection mechanism is commonplace in many industrial sectors and has particular applications to mixing and heat transfer processes.

This classical fluid mechanics problem has attracted a great deal of attention from numerous authors over many decades. Indeed, this remains an active area of investigation for UK researchers as is evidenced by [1, 2]. Recent studies [3, 4] have shown that the boundary-layer flow of a globally non-Newtonian fluid can be markedly different to that of a regular Newtonian fluid. A natural extension of this work is to ask ‘How will Newtonian boundary-layer flows be affected when a non-Newtonian fluid is injected at the wall?’ Using advanced simulation techniques, we aim to address the following problem: ‘Is it possible to use non-Newtonian injection to promote boundary-layer transition (advantageous for mixing and heat transfer) or, equally, to delay it?’

The proposed investigation aligns with a strategic aim of the ‘Boundary layers and complex rotating flows’ SIG, namely, diversifying application areas beyond aerospace. As part of this proposal, Dr Griffiths will initiate validation discussions with non-Newtonian experimentalists (fellow ‘Non-Newtonian fluid mechanics’ SIG members). He will also seek matched funding via the Centre for Flow Measurement and Fluid Mechanics Invited Researcher Scheme. This will allow Dr Davies to visit Coventry after the SRV has taken place.

The proposed project amalgamates expertise from the ’Boundary layers and complex rotating flows’ and the ’Non-Newtonian fluid mechanics’ Special Interest Groups. Recent SIG meetings have highlighted the fact that there appears to be numerous shared interests between these groups and we expect that dissemination of our initial findings will serve to improve cohesion between these two SIGs.

References

[1] Hewitt, R. E., Duck, P. W. & Williams, A. J. (2017) Injection into boundary layers: solutions beyond the classical form, J. Fluid Mech., 882, 617–639.

[2]Williams, A. J. & Hewitt, R. E. (2017) Micro-slot injection into a boundary layer driven by a favourable pressure gradient, J. Eng. Math., 107, 9–35.

[3] Griffiths, P. T. (2015) Flow of a generalised Newtonian fluid due to a rotating disk, J. Non-Newt. Fluid Mech., 221, 9–17.

[4] Griffiths, P. T. (2017) Stability of the shear-thinning boundary-layer flow over a flat inclined plate, Proc. R. Soc. A, 473, 2017.0350.

Heat dissipation in electronic components is becoming a critical issue due to the rapid increase in heat flux and the demand for ever-smaller components. The heat flux of electronic chips may exceed 400 W/cm^2 and high performance cooling techniques are required to keep device temperatures low for acceptable performance and reliability.

The microchannel heat sink (MCHS) is a concept well-suited to many electronic applications because of its ability to remove a large amount of heat from a small area. However, its heat transfer rate may be limited by the transport properties of the working fluid, such as its thermal conductivity.

One of the most advanced methods to improve the thermal conductivity of the working fluid is the addition of nanoscale solid particles: by adding 5% of the working fluid mass in nanoparticles, the liquid thermal conductivity can be increased by up to 20%.

However, it is well known that the addition of nanoparticles in a working fluid will not only result in an improvement in the liquid thermal conductivity but will also influence the liquid viscosity and density, and these two properties will directly influence the two-phase mixture of liquid and nanoparticles.

The present study is motivated by the need to understand the constraints and issues related to the use of nanofluids in MCHS.

The University of Manchester is well-known for its research and contribution to topics in fluid-structure interaction, and theoretical and numerical wave modelling including the SPH method. Dr. Masoud Hayatdavoodi of the University of Dundee is an expert in Green-Naghdi (GN) Equations and their application to wave-structure interaction problems. In this SRV, Dr. Hayatdavoodi will visit Dr Rogers in the School of Mechanical, Aerospace and Civil Engineering to explore possible collaborations between Manchester and Dundee in environmental fluid mechanics, in particular in the fields of wave-structure interaction, nonlinear wave theories and marine renewable energy. Dr. Hayatdavoodi will give a presentation in the Water, Ocean, Coastal and Environmental Engineering with Geotechnics (WOCEE-G) Seminar series entitled "Wave Loads on Coastal Structures: The Nonlinear Shallow Water Wave Equations". The talk is mainly concerned with the advancements on the application of the GN equations to some nonlinear wave-structure interaction problems.

We will investigate the feasibility of using self-assembly in complex fluids to construct a novel metamaterial from simple colloidal ingredients. It will be a colloidal alloy of microgel particles, a proportion of which contain super-paramagnetic (SP) cores. We speculate that the material's acoustic and mechanical properties (e.g. stiffness, viscoelasticity) will be tunable via two routes: (i) varying osmotic pressure to swell the polymeric microgel; and (ii) applying an external magnetic field inducing dipole-dipole interactions between the SP cores.

An inter-dependence between the metamaterial’s nontrivial magnetic response and its sensitive structure, each delicately poised at the boundary between order and disorder will engender new phenomena, mediated by mixed magneto-mechanical waves. This will require non-trivial theoretical modelling.

Such materials' novelty will derive from their ease of fabrication by self-assembly, together with the interactions between their magnetic, structural and fluid properties. They would potentially be cheap and simple to produce in large quantities. The resulting metamaterials could find applications in fields as diverse as energy conservation (via thermal properties), nanomanufacturing, acoustics (tunable sound insulation), wearable technology and healthcare (tunable stiffness allowing bespoke appliances).

The path-finding feasibility study will allow us to develop fuller plans and well-informed proposals for funded research. Results will be shared through the "Fluid mechanics of nanostructured materials" SIG and "Non-Newtonian fluid mechanics" SIG.

The objective of this trip is to build and test a novel Fluid Electric Generator using an unexpected flow instability that we recently discovered. In particular, while at Cambridge, we aim to use a new flow-to-energy approach that allows us to convert low-grade heat (5-150°C) into electrical energy.

In the oil and gas industry, rock particles generated during any drilling operation must be removed with a suitable non-Newtonian fluid to prepare the drilled well for eventual production. Multiphase flow simulations that describe the annular particle transport mechanism during Underbalanced Drilling (UBD) operations are scarce. This is due to the added complexity introduced by the flow of a gas phase from the reservoir to the wellbore. Modelling this complexity is paramount to the design and operation of the UBD process. Thus, it is important to know the particle velocity distribution, particle dispersion behaviour and pressure drop variation under this condition compared to a two-phase scenario (fluid and particles only), for which many published studies exist [1,2,3,6]. Combining with the CFD expertise of the research group at Cranfield will provide an opportunity to tackle effectively this multiphase flow problem in the Oil and Gas industry [4, 5].

Another important feature is that effective wellbore cleaning (rock particle removal) and the mitigation of intense particle deposition often require the application of high fluid velocities, thus resulting in turbulent transport conditions [2]. Previous studies of this transport phenomenon using the Lagrangian-Eulerian approach involve coupling the Lagrangian tracking of computational particles to a continuous flow description based on the Reynolds-Averaged Navier-Stokes equations [5, 6]. It is however possible to couple the Lagrangian description of the particle phase with more advanced numerical techniques such as Large Eddy Simulation for the fluid phase description [7]. By doing this, we expect to obtain a more accurate description of the flow field, particularly under turbulent conditions. The advances in numerical computations and high performance computing at Cranfield will help to achieve this objective.

References

[1] Epelle, E.I. and Gerogiorgis, D.I., 2017. A multiparametric CFD analysis of multiphase annular flows for oil and gas drilling applications. Computers and Chemical Engineering, 106, 645–661.

[2] Epelle, E.I. and Gerogiorgis, D.I., 2018a. Transient and Steady State Analysis of Drill Cuttings Transport Phenomena under Turbulent Conditions. Chemical Engineering Research and Design, 131, 520–544.

[3] Epelle, E.I. and Gerogiorgis, D.I., 2018b. CFD modelling and simulation of drill cuttings transport efficiency in annular bends: Effects of particle sphericity. Journal of Petroleum Science and Engineering (accepted after minor revision).

[4] Loyseau, X.F. and Verdin, P.G., 2016. Statistical model of transient particle dispersion and deposition in vertical pipes. Journal of Aerosol Science, 101, 43–64.

[5] Loyseau, X.F., Verdin, P.G. and Brown, L.D., 2018. Scale-up and turbulence modelling in pipes. Journal of Petroleum Science and Engineering, 162, 1–11.

[6] Akhshik, S., Behzad, M. and Rajabi, M., 2015. CFD–DEM approach to investigate the effect of drill pipe rotation on cuttings transport behavior. Journal of Petroleum Science and Engineering. 127, 229–244.

[7] Subramaniam, S. 2013. Lagrangian–Eulerian methods for multiphase flows. Progress in Energy and Combustion Science, 39(2), 215–245.

The SRV will further build on Dr Majumdar's scientific connections with the Complex Fluids Group, led by Dr Ian Griffiths at the University of Oxford, and build new collaborations with Professor Muench and Dr Kitavtsev on active biological fluids at the University of Oxford. The main scientific aims of this SRV are to model and mathematically characterize the complex interplay of order, fluid flow, confinement effects, external fields and activity in nematic liquid crystals, which are classical examples of anisotropic materials that combine the fluidity of materials with the long-range orientational order of solids. More precisely, the project focuses on -

[1] modelling backflow in nematic microfluidics as a function of temperature and material constants, building on the scientific outputs from Dr Majumdar's first SRV to Oxford;

[2] modelling ion transport in liquid crystal devices in collaboration with the Complex Fluids Group at Oxford and Merck ( a leading industrial company in liquid crystals) and

[3] modelling the effects of activity on the "passive" nematic solution landscape in collaboration with Professor Muench and Dr Kitavtsev at Oxford, which is particularly relevant to biological systems.

When a micro-droplet is placed in the path of surface acoustic waves (SAWs), longitudinal waves enter the droplet and cause internal streaming together with an increase in droplet temperature [1]. This increase is dependent on the type of piezoelectric material, fabrication of the IDT, frequency of the wave, viscosity of the droplet, etc. Much work has been done using a LiNbO3 (Lithium Niobate) substrate, but there is a knowledge gap in the use of devices based on ZnO (Zinc Oxide), which have many potential uses in microfluidic applications. ZnO thin films can be used for different SAW and FBAR devices on a range of substrates due to their high crystal quality, uniformity in film microstructure, and smooth surface and low roughness [2], making them versatile, flexible and even wearable.

The aim of this SRV is to investigate how Rayleigh, Sezawa and Lamb waves interact with liquid and particles in acoustofluidics applications using ZnO thin-film-based acoustic wave devices, and determine how much power applied to the IDT contributes to thermal change and how much to the internal flow. The wave mode affects the resonant frequency, and the frequency itself impacts the temperature uniformity in the droplet. For example, at higher frequencies, a SAW is quickly attenuated with less penetrating the liquid, resulting in poor temperature uniformity, while the opposite is true for lower frequencies. Polymerase chain reaction (PCR) is an important biological application that needs a homogeneous temperature [3], [4].

The work will include the following.

1. Visualize streaming by using 10 μm polystyrene particles and ZnO_Si-based device (zinc oxide on silicon) with Rayleigh and Sezawa modes, followed by ZnO_Al-based thin film devices with Lamb waves. Then obtain the droplet temperature distribution using a FLIR thermal camera, and finally assess how much streaming contributes to the droplet temperature increase.
2. Change the thickness of Al to modify the resonant frequency of the waves and change wave modes.
3. Obtain energy balance by measuring power input given to the IDT and output after passing through the IDT by using oscilloscope and power meter.

References

[1] Roux-Marchand, T. et al. Rayleigh surface acoustic wave as an efficient heating system for biological reactions: Investigation of microdroplet temperature uniformity. IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 2015. 62(4), 729-735.

[2] Fu, Y. et al. Recent developments on ZnO films for acoustic wave based bio-sensing and microfluidic applications: a review. Sensors and Actuators B: Chemical, 2010. 143(2), 606-619.

[3] Miralles, V. et al. A review of heating and temperature control in microfluidic systems: techniques and applications. Diagnostics, 2013. 3(1), 33-67.

[4] Roux-Marchand, T., et al. Temperature uniformity of microdroplet heated by buried surface acoustic wave device. In 2014 IEEE International Ultrasonics Symposium (IUS), pp 1956-1959.

This SRV will provide a networking opportunity and facilitate knowledge transfer between the research groups working on foam physics at Loughborough University and the Smart Material and Surface group at Northumbria University, working on 3-dimensional foam-based material development. The main focus of the SRV will be the characterisation of nanosolids in highly-diluted systems and their impact on the foam structuring mechanism when in the liquid state.

This project addresses the fundamental problem of nanosolid attachment to the water-air interface, and therefore can have great impact on the recovery of nanoparticles recovery (applied especially to detergents, drug delivery and waste treatment) as well as nanoparticle sensor design.

The preliminary outcomes anticipated from the SRV will be used in an EPSRC grant application, scheduled for submission by Autumn 2018. Further work is expected to result in a paper ready for submission by Winter 2018.

The researchers at Oxford have expressed interest in using pressure-sensitive paint in their experimental measurement campaigns; however, their current methods involve the use of commercially-available hardware and chemicals. Dr Mark Quinn specialises in these methods and their application in almost all flow regimes, and has built custom systems and software to measure flow fields in challenging environments. The aim of this visit is to investigate how the two research groups could work together by leveraging their individual expertise.

The University of Manchester also has a hypersonic tunnel, and its uses and comparable work at Oxford will be discussed with the help of Mr Tom Fisher, who has extensive experience of working in experimental facilities such as these, both in the UK and at DLR (Germany).

The researchers will discuss methods of solving the challenges associated with high-speed wind tunnel testing, particularly around the use of field sensors, and also to run a short internal seminar to raise awareness of each group’s work.

A two-week research visit by Dr Davies Wykes to the University of Bristol will support the timely conclusion of a multi-year collaboration studying irreversible processes in density-stratified mixing. Small-scale, irreversible conversion of energy is poorly quantified by existing metrics, especially where domain boundaries tend towards infinity. This project gets to the heart of what mixing means, and proposes a probabilistic interpretation of turbulent diffusion to calibrate reduced-order models for vertical mixing.

Many asymptotic models for fluid flows rely crucially on a ‘thinness’ criterion: that internal structures in flows vary slowly compared to the curvature of the underlying substrate. Unfortunately, many industrially relevant flows violate this criterion.

AW recently demonstrated [1] a method for relaxing the constraint, and producing accurate asymptotic models even for thick flows. However, this work only examined flows at zero Reynolds number. It is anticipated that flows with inertia will provide a significantly more stringent test of the methodology, and are more representative of a much wider range of physical flows.

AW knows how to produce the relevant models and RC has significant expertise in the direct numerical simulation of interfacial flows across a range of scales and parameter regimes, allowing both the validation of the asymptotic models and the identification of their range of applicability. It is expected that the SRV will permit significant progress to be made on this problem.

Reference

[1] Wray, A.W., Papageorgiou, D.T. and Matar, O.K. Reduced models for thick liquid layers with inertia on highly curved substrates. SIAM Journal on Applied Mathematics 77.3 (2017), 881-904.

The SRV will focus on the characterisation and understanding of the unique flow phenomena associated with turbulent pulsatile puffs by using novel static flow control strategies, including

• manipulating their unstable azimuthal transition through nozzle optimization
• their characteristics of impingement onto a solid target

The former focuses on the mixing and mass transfer application, where the puffs are optimised to maximise the transportation distance. The latter underpins the heat transfer characteristics associated with flow-surface interaction.

The SRV will collect two sets of spatiotemporal-resolved experimental data in the large multi-functional puff generator at Durham:

1. Simultaneous scalar and velocity fields, to investigate the balance of mixing and momentum delivery by turbulent puffs of different geometries;
2. The flow field near the surface of the solid target, to assess the turbulence and hence the heat exchange ability of the puffs during impingement.

In addition, puff trains with various degrees of intermittency will be explored to seek optimal momentum delivery efficiency.

Particle-driven gravity currents occur in a variety of atmospheric and hydrological settings and pose a significant natural hazard. Recently, for example, powerful dust storms in India caused extensive damage to buildings and loss of life. This SRV will initiate a collaboration to explore the problem in the laboratory and to plan further work. The first part of the visit will focus on carrying out a set of experiments to develop insight into the processes that are responsible for structural failure within gravity currents. Particle tracking will be used to visualise internal flow structures for particles of different sizes. The appropriate parameters for such flows in air and water will be examined and, in addition, the possible application of the results to the impact of tsunamis on buildings will be investigated.

Subsequent meetings will focus on writing up the results of the work for publication in a high-quality journal and outlining proposals for future work. It is intended that this work shall begin a longer-term collaboration that will be extended to include additional partners from the departments of both collaborators. A proposal for this future work will be submitted to external funding bodies such as EPSRC.

A number of experimental measurements at very different length scales and geometrical configurations (Bayer & Megaridis, 2006, JFM 558; Fell et al., 2011, Langmuir 27; Park et al., 2012, JFM 707) suggest that a limiting value for the advancing contact angle exists, with value about 125~130°. The applicant (2016, EFMC11) showed that this angle is close to the singular value for the local similarity solution, resulting in infinite shear force and pressure. It is conjectured that (i) there will be strong resistance to the angle being close to the critical value, and that (ii) if the advancing angle is forced to pass the critical value, an unbounded increase in the shear force may trigger a burst of capillary waves. Such phenomena have not been documented before.

The SRV will document the anticipated phenomenon in collaboration with Dr Tanino in her state-of-the-art laboratory at the University of Aberdeen. A custom-made microfluidic experimental station will be adapted for this purpose. Dr Tanino has more than 6 years of experience in tuning the composition of oils to alter systematically the wetting characteristics of mineral surfaces, and experiments will be conducted using different combinations of liquid/liquid/substrate.

The acquired data and theory will culminate in a Journal of Fluid Mechanics submission. In the mid-term, we expect that the visit will serve as a stepping stone towards a joint EPSRC proposal on contact line motion in industrial settings.

This SRV will conduct proof-of-concept research to develop microfluidics-based soft material printing for next-generation flexible electronics. It will integrate Northumbria University (NU) experience in soft materials and microfluidics with the University of Edinburgh (UoE) sensor and microsystems fabrication expertise, leading to research publications and future funding opportunities.

The SRV will facilitate YL's initial visit to JT at UoE for five days, to produce microfluidics surfaces that can be used to pattern functional polymer utilizing UoE's microfabrication and characterization facilities. Patterned polymer samples will then have mechanical and optical tests carried out post-visit at NU. After the initial results are obtained, JT will make a few visits to NU, with optimized samples and assist with analytical measurements, discuss results and outline further sample fabrication requirements. These visits by JT will also be used to develop publication plans and begin preparation of a future funding proposal. A further visit will be made by YL to UoE to discuss progress on the joint funding proposal, with the goal of submitting in early 2019.

Explosions at basaltic volcanoes are commonly driven by the bursting of large gas bubbles that rise through a magmatic foam. We will investigate this process using Durham's novel X-ray tomography and radiography facilities to image bubble ascent through analogue foams, and then develop theory and simulations to explain the observations.

Biomass energy resources are currently attractive renewable fuels to replace fossil fuel combustions in utility boilers for hot water productions. However, the energy utilisation efficiencies of such biomass boilers are relatively low due to the large temperature difference involved for heat transfer. Alternatively, biomass thermo-power conversion technologies with advanced thermodynamic power cycles have been discovered to be promising options at present. CO2, as a natural working fluid, has been widely applied in refrigeration and heat pump system owing to its zero ODP, negligible GWP and superb fluid thermophysical properties, which can also be used in the thermodynamic power cycles. Nevertheless, there are significant challenges in the integration of biomass fumes with CO2 working fluid for advanced energy transfer, due to the different thermal properties that each fluid relies on. The aim of the proposed SRV is to use advanced experimental methods to investigate the combustion characteristics of different biomass fuels for further model setup. In particular, experimental research will be carried out the analysis of heat transfer characteristics between biomass fumes and CO2 working fluid through a shell-and-tube heat exchanger of a biomass-CO2 power generation system.

The University of South Wales houses a state-of-the-art biomass power generation test system with advanced CO2 thermodynamic power cycles, which has specific feature to investigate combustion and heat transfer between biomass fuels and CO2 working fluid through a shell-and-tube heat exchanger. The proposed SRV will be used to conduct a collaborative experiment with Prof. Yunting Ge in University of South Wales. The research outcomes of this collaborative experiment are expected to lead to a joint publication in the future and an EPSRC New Investigator Award application by the end of 2018.

To explore the role of urban buildings on the flow above them (and subsequently the flow around areas downwind) the wind tunnel (WT) has been a key tool. Recent work has started to consider variability of buildings and their impacts on flow regimes. With a few individual tall buildings surrounded by other shorted buildings the depth of the roughness sublayer (RSL) becomes deeper that creates a challenge for WT observations. It is possible to explore the details of the flows around the buildings with a large (e.g. 1:200) scale model in a WT (e.g. Hertwig et al., in preparation) but it becomes difficult to measure throughout the RSL and the inertial sub layer (ISL) because of WT limitations.

In this SRV we propose to explore the following.

1. 3D printing of a model that has been used in the WT (Hertwig et al., in preparation) at a smaller scale.
2. Use of this model in a WT and water tunnel to assess the overlap that can be measured between model scale. Ideally this would permit a link with earlier lower RSL and urban canopy layer (UCL) observations.
3. Primary goal: Investigate impact of (a model of) real tall buildings on the RSL to ISL flow characteristics for the development/ assessment of meteorological parameterisations.
4. Discuss possible proposal preparations

This visit concerns the hydrodynamic stability of non-Newtonian – and specifically viscoelastic – fluids in boundary layers, which have received much less attention than their Newtonian counterparts.

Being able to predict the transition to turbulence is crucial in industrial applications. Moreover, motivation for studying viscoelastic fluids at high Reynolds numbers can be found in the established phenomenon of turbulent drag reduction by dilute polymeric additive [4]. Some results have been obtained for the linear stability in channel flows: for example, Palmer and Phillips [3] studied the linear stability of the linear Phan-Thien-Tanner fluid model for plane Poiseuille flow. Regarding the stability of non-Newtonian fluids over an inclined wedge, Griffiths [2] recently investigated the shear-thinning effects on the stability of the flow over a flat inclined plate.

This project aims to expand the understanding of viscoelastic effects on the stability of boundary layers. Earlier work considered a fluid of second grade [1] due to the simplicity of its constitutive equation and the possibility to apply a boundary layer theory similar to Prandtl’s boundary layer theory. Elasticity in this model is shown to stabilise slightly the two-dimensional exponential (Tollmien-Schlichting) waves, to destabilise spanwise disturbances and to promote short-time growth of energy. We would like to start investigating the linear stability and transient behaviour of rheologically more complex fluids. Possible models that can be considered are the Maxwell, Oldroyd-B, Giesekus and Phan-Thien-Tanner models.

[1] Rivlin, R. S., Ericksen, J. L. (1955). Stress deformation relations for isotropic materials. J. Ration. Mech. An., 4, 323–425.

[2] Griffiths, P. T. (2017). Stability of the shear-thinning boundary-layer flow over a flat inclined plate. Proc. R. Soc. A, 473(20170350).

[3] Palmer, A. S., Phillips, T. N. (2005). Numerical approximation of the spectra of Phan-Thien Tanner liquids. Numer. Algorithms, 38, 133–153.

[4] White, C. M., Godfrey Mungal, M. (2008). Mechanics and Prediction of Turbulent Drag Reduction with Polymer Additives. Annu. Rev. Fluid Mech., 40, 235–256.

This project will quick-start experiments employing, for the first time, the state-of-the-art micro-bubble and hydrophobic microfluidic technology to investigate long-time behaviour of individual spermatozoa. This will exploit unique research experience in the Department of Mechanical Engineering at UCL on nano-engineering/micro-scale flows.

In this project, we will start a new collaboration to develop a mathematical method and numerical strategy to predict rare events in turbulent reacting flows. We will analyse a big data set from direct numerical simulation of a premixed flame. A data-driven clustering algorithm will be employed to find the physical precursors of autoignition kernels. The SRV will provide the unique opportunity for the host and visitor to work side by side on the project both on the mathematics and the coding.

Dr Lasagna will visit Dr Papadakis and Prof Chernyshenko at Imperial College, to continue work that was started at a recent Euromech Colloquium (EUROMECH 598, “Coherent structures in wall-bounded turbulence: new directions in a classic problem”, 29-31 August 2018, Imperial College London,). The purpose of the visit is to develop an understanding of the properties of new adjoint sensitivity methods for chaotic systems. In a fluid dynamics context, interest in these methods is driven by the need to develop new approaches for control and optimisation of fully developed turbulent flows, where traditional adjoint methods fail to provide correct sensitivity information.

The recent volcanic eruptions in Hawaii (May-June 2018) have highlighted the threat posed by lava flows, which progress downslope, seemingly unstoppably, driven by gravity and resisted by basal drag. While barriers to arrest and divert the oncoming flow have been historically deployed, they have had limited success and there is a fundamental challenge of what can be done to mitigate this hazard. In particular, can we create models of the flow dynamics to inform the optimal design of barriers?

This research project was initiated during July-August 2018 while Edward Hinton was a fellow at the Geophysical Fluid Dynamics programme at the Woods Hole Oceanographic Institute (WHOI), in which Hogg and Huppert were participating. Initial experiments performed at WHOI produced some intriguing results: they indicated the possibility of formation of a wake downstream of some obstacles, in some flow conditions, into which the viscous fluid does not spread, and competition between upstream ponding and flow deflection around discrete obstacles, which controls whether the obstacle is overtopped.

This SRV will be used to initiate a new laboratory campaign, to study these flows in more detail and make quantitative measurements of the interaction between free-surface, viscously-dominated flows and obstacles of varying sizes and shapes, and to refine the research questions and results.

Reynolds-robust discretisations of the Navier-Stokes equations are gaining increasing interest, due to recognition of the importance of exactly enforcing the incompressibility constraint in the numerical model. If this constraint is not enforced strongly, then the velocity solution is polluted by errors in the pressure. Moreover, this numerical error grows as the Reynolds number is increased. Despite their many appealing properties, efficient solvers for such discretisations are lacking, making them inaccessible to high resolution simulations.

In recent collaborative work (Farrell et al., 2018) initiated in a previous SRV (“Multigrid solvers for high Re stationary Navier-Stokes flow”), we have, for the first time, developed a mesh-independent, Reynolds-robust multigrid solver for the Navier-Stokes equations in three dimensions. However, this solver depends on the use of a discretisation which is not divergence-free.

The goal of this visit is to address this issue, by extending the solver to handle divergence-free discretisations. In particular, we will focus on the Scott-Vogelius element pair. For the lowest-order version of this element, a vital missing piece in our implementation is multigrid mesh hierarchies on barycentric refined meshes. In this visit, we will extend the existing multigrid support in Firedrake (www.firedrakeproject.org) to support this case. We also aim to improve the computational efficiency of an additive Schwarz patch smoother recently incorporated in PETSc (again with significant development initiated during the previous SRV), which will be critical to the fast implementation of our solver.

The resulting preconditioner will be documented and made available to the UK fluids community as part of the open source Firedrake software.

Reference
Farrell, Patrick E., Lawrence Mitchell, and Florian Wechsung (2018) An augmented Lagrangian pre-conditioner for the 3D stationary incompressible Navier-Stokes equations at high Reynolds number. Submitted.

The Northumbria team has developed a novel design of very high sensitivity optical fibre sensors, using tapered micro/nano SMS fibre structures, which are able to detect concentrations as low as 4 ppb ammonia in water.

To make such optical sensors applicable in a diagnosis context, the expertise of Prof Pamme’s group will be used to modify the sensors, combined with a microfluidic flow cell, to carry out sample clean-up, pre-concentration and bioassays.

Dr Wu will bring micro/nano SMS fibre sensors from Northumbria and, in collaboration with Dr Iles, will fabricate and test a range of chip devices during the visit.

It is envisaged that the fibre sensors developed by Dr Wu will allow the measurement of biomarkers in blood and urine with the high sensitivity needed for the early diagnosis of infectious disease (pathogens) and non-communicable diseases (cancer, heart conditions, neurological conditions).

Proof-of-concept studies in support of an RCUK grant bid, and further collaborative work, including discussions with industrial partners (such as Epigem Ltd), will also be carried out.

Reactive inkjet printing is an emerging manufacturing technology for which sufficient mixing between impacting and coalescing droplets consisting of different fluids is essential. However, recent studies have observed surprisingly little mixing between impacting and coalescing droplets of the same fluid (Castrejón-Pita et al., Phys. Rev. E, 2013), with droplets of different chemical composition still to be explored.

During the proposed SRV, experiments involving impacting and coalescing droplets of different chemical composition will be conducted, with direct relevance to reactive inkjet printing. Dr Castrejón-Pita, at the University of Oxford, has significant experience in experiments exploring the internal dynamics of impacting and coalescing droplets, in addition to the ultra-high speed cameras (colour and grayscale) and droplet generators required for this study. The visit will produce high-quality experimental data to complement numerical simulations developed at the University of Leeds, with the aim of improving the fundamental understanding of droplet mixing relevant to reactive inkjet printing.

The visit is concerned with the experimental investigation of the hydrodynamics of liquid jet impingement under industrially relevant conditions. The experimental set-up at the University of Manchester allows the jet and wall angles to be manipulated independently, generalising the cases studied in earlier experiments at Cambridge. The visit will also include training in techniques to measure film thicknesses of draining flows.

The Pre-Swirl Nozzle (PSN) assembly supplies cooling air to the high pressure turbine blade. The nozzles act to accelerate and swirl the flow so that the velocity of the air matches the high pressure disc. Two measurements are performed on each component: the flow rate at a certain pressure ratio (typically around PR=1.5); and the outlet angle of jet from the horizontal. The tests are required to ensure that the vane outlet angles are uniform for each set, and that each PSN set produces consistent angles.

A production-testing jig is in development to allow each PSN assembly to be tested within a 60-second span. The technique for measuring the flow rate is at a mature TRL, but the jet angle measurement is time consuming, not repeatable and prone to operator error. Furthermore, the angle measurement cannot be applied simultaneously to each PSN vane outlet jet, increasing the quality control test time.

This visit to the Rolls-Royce Heat Transfer Facilities will inform the application of Background-Oriented Schlieren (BOS) to quantify jet outlet angles from the PSN assembly.

BOS also has the potential to provide additional diagnostic information that can be used in development, e.g. quantification of the density field.

Resonant-microfluidic biological-cell-suspensions manipulation chambers are being developed for continuous industrial processing and sample preparation upstream from sensors. Currently chamber drives are glued-on Lead-Zirconate-Titanate-transducers. This visit is to test the feasibility of depositing ZnO thin-film-transducers directly onto the chamber. Avoiding glued-on transducers will increase reliability, simplify construction and extend design options.

Why is this chamber important?
In 1-10 MHz resonant sound fields, suspended biological cells move to the nodal planes. This type of manipulation can be used to perform filtration, separation and cell-positioning. These operations are central to the bio-processing industries and also for sample preparation stages upstream from sensors. Monitoring suspensions is essential for medical labs through to environmental field locations. Such acoustofluidics processing could become a widely used core operation but, despite many influential proof-of-principle experiments, reliability has remained an issue.

What is the challenge for the current designs?
Most systems are constructed using glue to fix the Lead-Zirconate-Titanate-transducers, or PZTs, to the chamber walls. Gluing is not a well-controlled process: variability in thickness and subsequent sensitivity to ultrasound introduces significant variability, preventing quantitative use.

Why is it critical to use ZNO films?
PZTs are well established workhorses for producing ultrasound in large devices however acoustofluidic chambers are small (typically the fluid layer is 0.2-0.75mm). A 1 MHz PZT requires sintering at >1000°C and poling at 4000 V for 10 days. Manufacturing in situ on a plastic chamber is not possible: the PZT is manufactured separately then glued. ZnO films on the other-hand can be deposited directly onto some chamber components. Use of ZnO films for 1-3 MHz cell manipulation chambers appears to be novel. It may introduce several new design options for the chambers by enabling driving at precise locations.

Dr Hawkes will visit Northumbria University to learn the processing method for constructing ZnO transducers. These transducers will be used to drive 1-3 MHz acoustic cavities, and PIV will be used to compare systems driven by deposited ZnO and glued PZT. If time allows, the chamber walls driven by thickness mode and transverse mode waves will be compared.

The main purpose of this short research visit is to analyse the near-field turbulence of jets with different nozzle geometries. The three-dimensional velocity vector fields obtained from time-resolved tomographic particle image velocimetry (PIV) will be examined with statistical techniques and dedicated mathematical algorithms. The ultimate research goal is to identify a relationship between the nozzle geometry and the turbulent structures responsible for noise generation.

This SRV aims to perform experimental and numerical evaluation of the acoustic sources and of their propagation for the relatively unexplored case of high-thrust jets, improving understanding of their near and far sound fields.

Cold-air experiments will be performed at the recently commissioned University of Leicester anechoic chamber, complementary to tests completed at QMUL. A different microphone array to that employed at QMUL will be used to confirm the earlier results. This will test the sensitivity of common cold-jet flow and noise measurements to the facility and measurement system.

The high-speed jet noise tests at QMUL showed that crackle has high skewness in both its pressure wave-form and its derivative. In contrast, jet screech has rather lower skewness in its derivative, which is not consistent with the current understanding of screech as a highly non-linear process.

The visit will also undertake joint computational and experimental data analysis using the high performance computer cluster Alice2 (5000 cores) at the University of Leicester.

Clump formation is an essential precursor for many acoustofluidics applications: it enhances filtration, improves sensor detection limits and increases reaction rates. However current models cannot accurately predict clump size or location – both are products of the acoustic radiation force and acoustic streaming. Numerical streaming models are beginning to help, but precise experimental verification is difficult. This leaves acoustofluidics as an unusable tool wherever a highly quantitative output is required.

Experimental systems which are easy to adjust will be used to pinpoint efficient models for predicting the size and location of the clumps.

In the context of ground vehicle aerodynamics, platooning is the arrangement of two or more vehicles in a formation that results in a reduction of the overall drag of the vehicles compared to the combined drag of each in isolation.

Part of the challenge in studying vehicles in platoons is that conventional wind tunnel-based approaches require a compromise between the number of vehicles in a given configuration and their overall scale. This often means there is an unsatisfactory number of vehicles tested or that the scale of the vehicles results in loss of detail and large differences in Reynolds number compared to full-scale models.

Recently, at Northumbria University, and separately at the University of Birmingham, alternative approaches to wind tunnel testing involving full-scale on-road testing and scale moving models (the TRAIN*** rig) have been used to investigate platooning road vehicles. These methods overcome many of the limitations put in place by more conventional wind tunnel-based approaches, although they still have their own drawbacks. The purpose of this research visit is to share ideas about novel moving model approaches to aerodynamic testing and organise a collaborative research bid on the subject of platooning. Other novel methods involving moving model experimentation are currently being planned to expand research further in this area, and so sharing the current expertise will help to accelerate this important research topic.

***Transient Railway Aerodynamics INvestigation

We will pursue and conclude a collaborative project for theoretical and experimental analysis of flame propagation in high intensity turbulence. Flame surface measurements obtained in Leeds using a 3D laser imaging technique will be analyzed in the context of a theoretical framework developed in Cambridge.

The applicant’s research focuses on modelling internal nozzle cavitating flows. Currently, a two-phase compressible model with an explicitly transported volume fraction and a mass transport phase change model applied across the interface is being developed in the open source code OpenFoam. A future objective is to implement a third phase into this model so that external spray formation simulations can also be realised. This model will form the basis of a unified approach to modelling spray dynamics in a holistic manner (from in-nozzle to spray evaporation). The SRV will contribute to achieving this goal.

The model currently under development implements direct interface capturing of the vapour and liquid area, which increases the computational cost. Dr. Navarro-Martinez is working on a related project for spray formation and has developed an indirect methodology for capturing spray/air interfaces using a probabilistic sub-grid-scale methodology based on the concept of the surface density evolution. The aims of the visit are therefore: a) familiarisation with this novel methodology; and b) exploring the possibility of extending this approach to the modelling of cavitating flows.

Because accurate measurements of roughness-induced drag remain cumbersome at industry-relevant Reynolds numbers, it is necessary to use turbulence models. However, the lack of accurate models for the roughness elements means it is still necessary to solve the fine details of the flow in their vicinity.

The group at Glasgow have recently developed an algorithm capable of generating realistic bio-fouled surfaces and have carried out several direct numerical simulations on such surfaces. This presents an ideal scenario to test and validate the ongoing work at Southampton on the turbulence modelling front of this problem.

Thus, in summary, the goal of the SRV is to incorporate the hybrid RANS/DNS models developed at the University of Southampton into the numerical solver developed at the University of Glasgow. The models can then be tested on a range of rough surfaces generated by an algorithm developed at Glasgow for which DNS results are available.

The aim of the SRV is to train the applicant in the use of the Parallel Moist-Parcel-In-Cell model. This code was recently developed in a collaboration with the Edinburgh Parallel Computing Centre (EPCC): it provides a hybrid parallel implementation of the Moist Parcel-In-Cell method which scales on thousands of cores. The method provides a way of simulating clouds in a fully Lagrangian (parcel-based) way, and was originally developed jointly by the Universities of Leeds and St Andrews. Initial funding was provided by the EPSRC LWEC Maths Foresees network, and a description of the method has recently been published in the Quarterly Journal of the Royal Meteorological Society.

Dr Böing was involved in the development of the parallel version. This involved an extensive refactoring of the code, which means some initial support is needed for researchers that have only worked with the previous version (which only used shared-memory parallelism). The applicant will visit the University of Leeds to implement his recent developments in the new parallel code, which will be an efficient way of learning to work with the new code.

The SRV will be used to obtain experimental data on droplet pumping on inclined surfaces as the angle of inclination of the surface is varied.  The pumping results from the interaction of the droplet with surface acoustic waves propagating along the surface. A high-speed camera will be used to capture the droplet motions. Droplet contact angle, internal streaming patterns and droplet velocity are the key parameters that will be measured in the experiments. The data obtained will then be used in comparisons with simulation results.

The University of Manchester's hypersonic wind tunnel can achieve Mach and Reynolds number ranges unavailable in the ICL supersonic wind tunnel. By using novel infrared thermography (IRT) techniques, high resolution measurements of surface heat transfer can be made on faceted test model, specifically cubes and cylinders. These data will be compared to CFD predictions, already obtained at Imperial, and will also serve as a valuable precursor to develop the IRT technique for its first application in the ICL supersonic tunnel following this SRV (planned for spring/summer 2019).

The combined experimental data sets generated in both the Manchester and ICL high-speed wind tunnels will provide unprecedented insight into the variation of hypersonic heating rates at a range of Reynolds numbers spanning two orders of magnitude and Mach numbers from 4-6. The data will prove invaluable in the development of novel hypersonic heating models for various faceted shapes.

The SRV will be used to obtain microfluidic videos and experimental data from the interactions between surface acoustic waves, fluid and particles in a microchannel flow. The aim is to investigate how the surface acoustic waves affect the fluid and particles in a continuous flow in a microchannel, using various channel designs in the experiments, and to compare the data with 3D simulation results. The experiments will study the effects of various parameters, such as wave power and wavelength, particle size, fluid properties and microchannel geometry.

When a microdroplet is placed on the path where surface acoustic waves (SAW) propagate, longitudinal waves enter the droplet and cause internal streaming. Along with streaming, the temperature of the droplet increases [1]. This increase in temperature is dependent on the type of piezoelectric material, fabrication of the interdigital transducer (IDT), frequency of the wave, viscosity of the droplet, etc. Much work has been done using a LiNbO3 (Lithium Niobate) substrate, but to the best of our knowledge, there is a gap on the use ZnO (Zinc Oxide) based devices, which have potential in different microfluidic applications.

The aim is to investigate interaction of Rayleigh, Sezawa and Lamb waves with liquid droplet using ZnO thin film based acoustic wave devices and determine how much power applied to the IDT is converted to thermal change and how much in the internal flow. By using different wave modes at different resonant frequencies, the temperature of the droplet changes. Other than wave mode, frequency has an important effect on the temperature uniformity of the droplet: at higher frequencies, the SAW is quickly attenuated and penetrates less into the liquid, resulting in poor temperature uniformity, while the inverse is true at lower frequencies. Polymerase chain reaction (PCR) is one of the important biological applications where a homogeneous temperature is important [2], [3].

The first phase of the work is to find the coupling mechanism between internal streaming and thermal impact when the devices are bent at certain angles (30°, 60°, 90°). Bent devices have many applications in drug delivery processes and lab-on-chip (LOC). The second phase is to get an energy balance: how much energy in terms of RF input power given to the IDT is absorbed by the droplet and how much is output.

REFERENCES

[1] Roux-Marchand, T., et al. ‘Rayleigh surface acoustic wave as an efficient heating system for biological reactions: Investigation of microdroplet temperature uniformity.’ IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 62(4), 729-735 (2015).

[2] Miralles, V., et al. ‘A review of heating and temperature control in microfluidic systems: techniques and applications.’ Diagnostics, 3(1), 33-67 (2013).

[3] Roux-Marchand, T., et al. ‘Temperature uniformity of microdroplet heated by buried surface acoustic wave device.’ In 2014 IEEE International Ultrasonics Symposium, pp. 1956-1959.

Surface Acoustic Waves (SAWs) are high frequency nanometre-scale vibrations that propagate along a solid surface and can drive liquid flows on the surface, thus providing multiple microfluidic functions including liquid mixing, transport, jetting and nebulisation. We have demonstrated SAW devices, made on piezoelectric films (e.g. ZnO/AlN) grown on flexible substrates, which are promising for integration with electronic circuitry for fully automated, low cost microsystems with good mechanical flexibility, and which have efficient microfluidic functions. However, the behaviour of SAWs in microfluidic applications at low temperature has not been addressed. It is therefore of interest to investigate the interaction between SAWs and a liquid/ice mixture, and furthermore the effect on icing and de-icing processes. In Nottingham University, the team has access to all the facilities necessary to conduct de-icing and anti-icing experiments and to study liquid droplet behaviour on various surface-treated substrates. The contact angles for liquid droplets on different treated surfaces will be measured, and the changes of contact angle during cooling and icing processes observed. The use of SAW devices for anti-icing and de-icing applications will also be considered.

The SAW devices will be transferred back to Northumbria to continue microfluidic characterisation on standard test-beds. These proof-of-concept data will be used in support of an EPSRC project, as well as in discussions with interested industrial partners (such as Epigem Ltd, a UK SME with interest in microfluidics products for healthcare applications and a long-term partner of the team in Glasgow).

The SRV will focus on the development of an integrated and validated methodology for the hydroelastic response of ice shelves. Five meetings and a presentation (Numerical Simulation Techniques for Ice Shelves) are planned. The project aims to combine advanced modelling concepts, special hydroelastic finite elements for oceanic wave induced ice flexure and data from field measurements (e.g. GPS data from the McMurdo Ice Shelf to be made available by Dr Willis) for model calibration. The proposed methodology will be able to predict: (i) effects of variable bathymetry and shoaling, (ii) hydroelastic dispersion, (iii) sub-ice shelf cavity wave fields, (iv) location and magnitude of maximum bending moments and shear forces and (v) hydroelastic resonances.

The SRV will be the preparatory phase (Phase 0) of an envisioned collaboration on the hydroelastic Finite Element modelling of Antarctic Ice Shelves. It will enable the researchers to draft the next phase of the project (Phase 1: development/validation of advanced hydroelstic models and finite element solution methodologies for ice shelves) and, to this end, pursue funding from relevant funding bodies.

The applicant is working towards her PhD on blood flow dynamics simulations in adult patients with congenital heart disease under the supervision of Dr A Kazakidi, University of Strathclyde. The project involves the investigation of the hemodynamic environment in these patients. Idealized two-dimensional models of the pulmonary bifurcation have been created and the effect of geometrical characteristics, such as the branching angle and origin, has been studied. Currently, the process is being extended to 3D geometries. This would greatly benefit from having patient-specific data from a younger population cohort in order to understand the development of the adult configuration.

Dr Schievano’s lab has established expertise in computational modelling of congenital hearts at the Great Ormond Street Hospital for Children. A unique library of patient-specific geometries is available in her group and would be a valuable source of identifying anatomical variations in the pulmonary bifurcation for this group of patients. During this SRV, these geometrical characteristics will be studied to help validate the idealised model results. More specifically, the centrelines of the patient-specific geometries will be identified and analysed using in-house software to post-process the geometric data.

The wave-particle duality of atoms allows matter waves to be used to build interferometric devices that can access higher frequencies than light. Nowadays, realizations of atomic interferometers are being performed in experiments of atomic Bose-Einstein condensates which involve splitting a (bright) soliton through an interaction with a narrow potential barrier in a harmonic trap. This leads to part of the soliton tunnelling through whilst the other part reflects off the barrier. Upon recombination of the solitons, slight phase shifts arising from the different distances travelled allow a high accuracy realization of an atomic interferometer. Such a realisation has been demonstrated very recently with experiments at the host institution. However, given the many parameters that can be varied and the limited information currently accessible to experimentalists, modelling of the soliton dynamics and how they interact with potential barriers that induce the soliton splitting and subsequent recombination is required. The Gross-Pitaevskii equation (which is the same model as the Nonlinear Schrödinger equation used in the study of water waves) provides an excellent description for capturing many of the phenomena that are observed in these experiments. We plan to perform simplified theoretical modelling combined with detailed numerical simulations of the observed phenomena. This visit will initiate a collaboration that has emerged from discussions at some of the Quantum Fluids SIG meetings.

In recent years, there has been great interest in the development of specialised asymptotic techniques to study physical problems where exponentially small effects are crucial in determining certain features. In such problems, it is often the case that these effects are beyond all orders of traditional perturbative approaches, and thus techniques in exponential asymptotics are required.

This SRV will initiate a new collaboration to apply these specialised asymptotic methods to problems in geophysical fluid dynamics. Our initial focus will be on equatorial waves, which propagate along the equator but are trapped in latitude (with exponentially decaying tails). These waves are important in various atmospheric and oceanic phenomena, such as El Niño and the organisation of tropical convection. However, it has been shown numerically (by John Boyd) that the equatorial Kelvin wave is susceptible to an instability with exponentially small growth rate in a weak shear flow, while the other equatorial waves remain stable. We aim to develop the corresponding exponential asymptotics. Once the mathematical (and physical?) structure is understood, we hope to identify other geophysical problems with similar instabilities.

The SRV will discuss the development of a novel reduced-order predictive reservoir model that reduces the computational time drastically, often by four orders of magnitude. Dr Yingfang Zhou leads the reservoir modelling group at University of Aberdeen, and has strong connections with oil and gas companies both in the UK and overseas. During the visit, we are going to work together on the fast, novel reduced-order model (ROM) and deep learning for the numerical simulation of multiphase flow in subsurface geological domains. In addition, we will discuss in detail joint proposals to secure funding both from research councils and the petroleum industry.

We will exchange some of my ideas of fast predictive modelling methods based on deep learning. An effective deep-learning-based ROM will be achieved by extracting a set of optimal basis functions from the system and using deep learning to deduce the fluid dynamics in a reduced space. The fast response of ROM provides a convenient way of performing computationally intensive tasks such as: sensitivity analysis, history matching and uncertainty quantification and provides a possible way to quantify model error and discretisation error. A non-intrusive reduced-order reservoir model for multiphase flow in subsurface geological domains will be discussed. The non-intrusive ROM does not need to access the source code of the original reservoir model.

Flow visualization is an essential tool in experimental fluid mechanics. Fluid flow patterns can be observed by various techniques to give insight into the underlying flow phenomena. Importantly, analysing experimental measurements can yield useful quantitative data that play an important part in the understanding of fluid mechanics. High-speed cameras typically form the basis of flow visualization techniques; however, they are expensive and therefore are mainly restricted to research teams.

A flow visualization system based on mobile phones has been developed by Emekwuru and his team and has been applied to low-pressure sprays from domestic devices. During this proposed research visit, the flow visualization results for water and water-based nanofluid spray cooling systems will be compared for both the mobile phone-based and the traditional high-speed, camera-based, laser measurement systems (making use of Brighton’s spray characterisation laboratories).

Students have been assigned for the study, and their comparative understanding and ease-of-use of both techniques will be recorded. Primary data on the extent to which mobile phone-based flow visualization systems can be used as alternatives to a high-speed camera-based system, or the possibility of using them as tools for preliminary studies for both research and industry, and as flow visualization teaching tools for high school or undergraduate classes, will also be evaluated. These aspects will be included in a planned EPSRC proposal.

While slip flows in shale gas reservoirs have been studied extensively, little is known about slip properties of the porous walls of automotive particulate matter filters. The aim of the visit is knowledge transfer between these two well-separated areas of research.

Slip flows in porous media have become important in the automotive sector because of the introduction of gasoline particulate filters. Coventry University have an ongoing research programme on filtration flows, and recent experimental results (Aleksandrova et al., 2018) show that the slip effect is more important than was previously believed. In petroleum engineering applications the topic has been extensively studied. Prof Jamiolahmady's group has an outstanding track record in studying slip flows in porous media (Moghaddam & Jamiolahmady 2016) at high pressure and constant temperature.

Knowledge transfer between these areas is not straightforward, as the permeability and slip in petroleum applications are mostly affected by the porous medium geometry and stresses. In automotive applications, the high temperatures cause gas rarefication and slip. Thus, while the key non-dimensional groups (e.g. Knudsen number) are similar, the dependence of slip coefficients on the temperature and inertial effects needs to be investigated in more detail.

The high-temperature flow facilities at Coventry and the porous media related experimental facilities and expertise at Heriot-Watt can be used for slip flow characterisation. Combined with rarefied gas modelling and analysis, such a study will give a unique insight into the slip effect in various conditions, including those relevant to filtration flows, and provide a basis for further studies. The aim of the visit is a search for overlap between the two applications and the sharing of knowledge about experimental and modelling challenges and solutions. The three applicants represent areas of research involved: experimental, modelling and rarefied gas flow dynamics. The expected outcome is scoping a pilot experimental/numerical project which will result in joint publications and future grant bids.

The SRV will initiate a new collaboration to develop textile-based smart devices with enabled functions and enhanced flexibilities, which hold a great potential to advance current technologies in wearable devices. It is an excellent networking opportunity to understand some significant questions in smart device manufacturing, particularly in droplet and flow interactions with bio-inspired surfaces and textile fibres. Some preliminary outcomes may be anticipated from this SRV program, based on which we could jointly submit an EPSRC grant application.

Circulating tumour cells (CTCs) are relevant to both primary and metastatic tumours, and are regarded as biomarkers in diagnostics, prognostics and therapeutics for tumours. Collection and interrogation of these ‘cargo-cells’ would open the way for novel therapeutic strategies. A critical issue when acoustically resolving and sorting CTCs is the amount of acoustic power that may be applied. ZnO piezoelectric films function at a broad temperature range allowing significantly higher acoustic-power to be applied in a single lab-on-chip device. The proposed visit will combine the acoustofluidic research for sorting CTCs at Cardiff University with the ZnO research capacity at Fu’s lab to increase both the sorting resolution and efficiency in CTC separation. The pilot data will be collected for preparing a joint journal publication after the visit.

During this visit, a mounting system for holding a ZnO film for generating surface acoustic wave (SAW) and a printed-circuit-board (PCB) electrodes will be developed. The ZnO film and the PCB electrodes are stacked to form a sandwich structure using screws on the sides, which allow radio frequency signals to drive the ZnO film to generate SAWs. A microfluidic channel will be bonded to the ZnO film, which will be continuously monitored by an inverted microscope to confirm the actuation produced on samples.

In order to test the ZnO SAW chip set-up, polystyrene microspheres of typical size for cells in the blood will be used. Furthermore, optimisation to the chip will also be investigated during the visit. This will be focused on device efficiency, heat generation in the fluid and particle velocity. Parameters including maximum input power, thermal effect, standing SAW formation and bonding with microfluidic channels will be characterised and validated.

The aim of this SRV is to investigate the possibility of using the OpenSBLI codebase, developed at the University of Southampton, to formulate automatic code generation and source-to-source translation capabilities for the Xcompact3d computational fluid dynamics framework. These capabilities are essential for the efficient transition to future high performance computing architectures, in particular advanced graphics processing units capable of exascale performance.

The SRV will take place at Aberystwyth University, Wales, UK. It aims to develop two-dimensional foam flow simulations applying the viscous froth model. Specifically it seeks to obtain equilibrium and non-equilibrium states for low to moderate flow velocities through surface energy minimisation in foam systems using Surface Evolver software.

The study of microfluidics has applications in industries such as pharmaceutical, medical treatment, food, cosmetic, oil recovery and soil remediation [1]. In particular, this SRV concerns the microfluidic rheological properties of a multiphase fluid, specifically liquid foam, which has been widely studied by Professor Simon Cox’s research group in recent years [2]. The rich rheological properties of liquid foams can be captured by using a two-dimensional model known as the viscous froth model (VFM) [3].

The VFM balances the curvature of the foam film with the pressure difference across it, converting any mismatch between these forces into film motion, thereby leading to viscous drag forces [4]. The VFM predicts that an infinite train of bubbles flowing in a channel under certain configurations is intrinsically stable [5]. In contrast, a small number of bubbles flowing in a channel can suffer topological transformations: the configuration is thereby unstable [6]. In order to determine the stability transition, it is necessary to validate and improve an N-bubble simulation (using “Surface Evolver” simulation methodologies, currently employed at Aberystwyth), with the number of bubbles N being varied to explore the effect of this parameter upon stability. Results can be benchmarked against an analytical approach currently being developed during Torres-Ulloa’s PhD. Moreover, results are expected to have applications in medical treatment (schlerotherapy), improved oil recovery and foam-based soil remediation.

REFERENCES

[1] W. Drenckhan, S. Cox, G. Delaney, H. Holste, D. Weaire, and N. Kern ‘Rheology of ordered foams—on the way to discrete microfluidics’ Colloids and Surfaces A: Physicochemical and Engineering Aspects, 263(1-3), 52–64 (2005).

[2] D. Vitasari and S. Cox ‘A viscous froth model adapted to wet foams’ Colloids and Surfaces A: Physicochemical and Engineering Aspects, 534, 8–15 (2017).

[3] P. Grassia, G. Montes-Atenas, L. Lue, and T. Green ‘A foam film propagating in a confined geometry: analysis via the viscous froth model’ The European Physical Journal E, 25(1), 39–49 (2008).

[4] T. Green, P. Grassia, L. Lue, and B. Embley ‘Viscous froth model for a bubble staircase structure under rapid applied shear: An analysis of fast flowing foam’ Colloids and Surfaces A: Physicochemical and Engineering Aspects, 348, 49–58 (2009).

[5] S. J. Cox, D. Weaire, and G. Mishuris ‘The viscous froth model: steady states and the high-velocity limit’ Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 465, 2391–2405, (2009).

[6] T. Green, A. Bramley, L. Lue, and P. Grassia ‘Viscous froth lens’ Physical Review E, 74(5), 051403, (2006).

We propose to combine the Moist Parcel in Cell method, developed by Dritschel and Böing, with an unstructured finite element model, developed by Shipton, to investigate sub-grid-scale modelling of moist processes in the atmosphere.