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 4 months. The next deadline is 31 January 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.