Micro & Nano Flows for Engineering
The micro & nano flows group is a research partnership between the Universities of Warwick and Edinburgh, and Daresbury Laboratory. We investigate gas and liquid flows at the micro and nano scale (where conventional analysis and classical fluid dynamics cannot be applied) using a range of simulation techniques: molecular dynamics, extended hydrodynamics, stochastic modelling, and hybrid multiscaling. Our aim is to predict and understand these flows by developing methods that combine modelling accuracy with computational efficiency.
Targeted applications all depend on the behaviour of interfaces that divide phases, and include: radical cancer treatments that exploit nano-bubble cavitation; the cooling of high-power electronics through evaporative nano-menisci; nanowire membranes for separating oil and water, e.g. for oil spills; and smart nano-structured surfaces for drag reduction and anti-fouling, with applications to low-emissions aerospace, automotive and marine transport.
EPSRC Programme Grant in Nano-Engineered Flow Technologies
Our work is supported by a number of funding sources (see below), including a 5-year EPSRC Programme Grant (2016-2020). This Programme aims to underpin future UK innovation in nano-structured and smart interfaces by delivering a simulation-for-design capability for nano-engineered flow technologies, as well as a better scientific understanding of the critical interfacial fluid dynamics.
We will produce software that a) resolves interfaces down to the molecular scale, and b) spans the scales relevant to the engineering application. As accurate molecular/particle methods are computationally unfeasible at engineering scales, and efficient but conventional fluids models do not capture the important molecular physics, this is a formidable multiscale problem in both time and space. The software we develop will have embedded intelligence that decides dynamically on the correct simulation tools needed at each interface location, for every phase combination, and matches these tools to appropriate computational platforms for maximum efficiency.
This work is strongly supported by nine external partners (see below).
- “Nano-Engineered Flow Technologies: Simulation for Design across Scale and Phase” EPSRC Programme Grant EP/N016602/1 (£3.4M)
- “The First Open-Source Software for Non-Continuum Flows in Engineering” EPSRC grants: EP/K038427/1 K038621/1 K038664/1 07/13-06/17 (£0.9M)
- “Multiscale Simulation of Interfacial Dynamics for Breakthrough Nano/Micro-Flow Engineering Applications” ARCHER Leadership Project 11/15-10/17 (£60k in supercomputer computational resource)
- “Skating on Thin Nanofilms: How Liquid Drops Impact Solids” Leverhulme Research Project Grant (£146k funding a 3-year PDRA)
- Airbus Group Ltd
- Bell Labs
- European Space Agency
- Jaguar Land Rover
- National Physical Laboratory
- Oxford Biomedical Engineering (BUBBL)
- TotalSim Ltd
- Waters Corporation
Latest news and blogs
David Emerson visited the State Key Laboratory of Hydraulics and Mountain River Engineering at Sichuan University (Chengdu, China) in May to discuss high performance computing and open-source software. He also gave a talk at the Parallel CFD conference in Kobe (Japan) on the inverse Magnus effect in high-speed rarefied flow.
James Sprittles was an invited speaker at the SIAM Student Chapter's Annual Conference at Imperial College London with a talk entitled Formation & Coalescence of Liquid Drops. A week later he gave a seminar in Engineering at the University of Cambridge on Singular Capillary Flows.
David Emerson has been successful in a recent joint EPSRC grant application (EP/N033841/1) with the University of Birmingham and the University of Surrey in a four-year project that seeks to develop an integrated multiscale hybrid framework for modelling complex two-phase solid-liquid flows.
Dr David Stephenson , Research Fellow, University of Warwick
On Thursday 6th May, researchers from the Universities of Warwick and Edinburgh were joined by Prof. Terry Blake (Emeritus Professor at the University of Mons) for a workshop on the "Molecular Modelling of Interfacial Dynamics". The workshop, hosted by Dr James Sprittles at the University of Warwick, provided a platform for discussing the prominent challenges involved in the simulation of micro-droplets and surrounding small-scale phenomena. Understanding the governing physics at fluid interfaces on the molecular level underpins a number of emerging technologies. For example, controlling the break-up and coalescence of droplets is crucial to the operation of 3D printers; understanding the wetting characteristics of droplets is important for producing uniform coating films which prohibit air entrainment; regulating the evaporation of solute-containing liquid droplets can reduce the damage to surfaces due to weathering; and understanding the fluid-gas interface near micro-structures such as carbon nanotubes is key for developing drag-reducing surfaces.
There were seven presentations in total, covering a range of topics from the fundamental physics of droplet break-up, impact, and wetting, to the use of multiscale methods and machine learning techniques to enhance molecular modelling capabilities. See below for the complete list of presentations, some of which were exquisitely captured by our official photographer (also James).
- A multiscale method for non-equilibrium gas flow simulation in high-aspect-ratio geometries (Duncan Lockerby)
- Accelerating a multiscale continuum-particle fluid dynamics model with on-the-fly machine learning (Dave Stephenson)
- Water flow through and over carbon nanotubes: applications to drag-reducing surfaces and water filtration membranes (Matthew Borg)
- Droplets evaporation and spreading: Molecular dynamics and sequential hybrid simulation (Jun Zhang)
- Dynamic wetting, forced wetting and hydrodynamic assist (Terry Blake)
- The dynamics of rarefied gases between colliding bodies (Alex Patronis)
- How liquid drops form (James Sprittles)
Also, there were biscuits. This is important.
Dr Srinivasa B Ramisetti, Research Fellow, University of Edinburgh
Recenlty I was reading a lot of research articles looking for information on slip lengths, for flow over hydrophobic/hydrophilic surfaces, reported from various experiments and numerical simulations in order to compare our slip length calculations extracted from simulations. There is a huge number of journal articles and reviews on slip length measurements from experiments and simulations. Below is a list of links to articles wherein slip lengths reported in different papers are collected and presented in a nice tabular fashion that is easy for one to refer.
Dr Stephen M. Longshaw, Research Fellow, Daresbury Laboratory
Much of the research undertaken within the Micro & nano flows group relies on sottware to compute new scientific results. There are plenty of examples of this within the history of this blog but one area of increasing importance is that of coupling codes together to solve multi-scle or multi-physics problems with more than one piece of software.
I have talked about coupling in the past but this time I wanted to briefly describe the concept of universal coupling. This idea is gaining traction at the moment within reearch communities around the world as well as major softare vendors, in a nutshell it is the idea of providing a universal interaction layer or glue that can stick together any type of software that solves a scientific problem to make up a larger whole to solve more complex problems than any of the individual components can solve on their own.
In the past I mentioned a number of software frameworks for solving multi-scale/multi-physics problems, one example was the MUSCLE2 library (link) which came from the European MAPPER project, the same consortia are also behind the H2020 funded COMPAT project. The intereseting thing about large solutions like these though is that their use and integration is inherently difficult because of the scale of what they are trying to achieve.
A number of solutions have become apparant that aim to solve the problem of universal coupling in a less intrusive way, in the past I mentioned EDFs PLE wrapper that comes as part of their Code_Saturne CFD software, this uses the concept of data transport at a set of points to allow transfer of data between solutions. The basic premise is that, regardless of the form of a solver (i.e. whether it is mesh based or not or whether it is a continuum solver or not) data can always be sampled at specific points and sampled data can be imparted on another solution from said points. From a software engineering perspective the challenge is not too great, of course like anything, to do it well is always a big challenge, but precedent for methods to achieve this sort of communication framework are well established. The key challange is to ensure loss of simulation fidelity at the point of coupling is either addressed or at least managed.
Primarily the key questions are:
1) How do I sample my solution at a specific point while maintaining the level of accuracy I desire/need (i.e. is it OK to perform a linear interpolation of surrounding cells/other discrete entities or is soemthing else required?)
2) How do I consume information stored in data set at a specific point within my solution (i.e. I know that an external force exists in my simulation domain at point x,y,z because a coupled simulation has told me so, but I have no exact discrete location within my solution that matches this point, is it OK to interpolate a new value from the coupled data and if so, using what method and if not, how do I ovecome this?)
Generic solutions like PLE take the stance that they provide the coupling mechanism but it is up to the individual software developers using it to define how data is imparted and consumed from the points.
A new solution has recently begun take-up within our group that starts to bridge the likes of MUSCLE2 and PLE by working in the simplistic manner of PLE but by being designed to allow developers to easily add their own data storage/impartment methods so the library can grow into a useful code base for many different method types. Originally developed within the Applied Mathematics division at Brown University in the USA, it is called the Multiscale Universal Interface (MUI) and is available to download from GitHub. In some ways, what MUI offers is fairly obvious when you take a step back, however its key strength is that it has been designed in a well-engineered manner to be both extensible and as light-weight as possible in that it is a header only C++ library (that currently provides wrappers for C and Fortran as well). It makes use of MPI for its communications but does so in a way that won't interfere with existing MPI comms, so multiple MPI applications can use MUI to interact.
The library is currently being tested within our group and should it prove a good way forward we will aim to collaboratively expand its current capabilities with the original research team at Brown, with the results making their way back into the software's repository.
In other news, a snippet of the Micro & Nano flows grouop work was recently on display at the 2016 emerging technology (or EMiT) conference at the Barcelona Supercomputing Centre in Spain. This conference looks to provide a platform for those using or developing the latest emerging trends in computing, be that software or hardware. We showed off some of the groups cutting edge work on the IMM method (coupling MD and DSMC) as well as some GPU porting work for our MD code.