Short Research Visits
UKFN is pleased to invite proposals for SRVs. The call is open to anyone working in fluid mechanics in the UK. The following pdf gives the context of the call and sets out the information you need to provide in your proposal:
Proposals will be assessed in batches every 2 months. The next deadline is 31 March 2018. In exceptional cases, it will be possible to consider funding outside the normal deadlines. Please contact us for a preliminary discussion.
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.