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).

Current Funding

  • “Nano-Engineered Flow Technologies: Simulation for Design across Scale and Phase” EPSRC Programme Grant EP/N016602/1 01/16-12/20 (£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 08/16-08/19 (£146k funding a 3-year PDRA)

Partnerships

  • Airbus Group Ltd
  • AkzoNobel
  • Bell Labs
  • European Space Agency
  • Jaguar Land Rover
  • Oxford Biomedical Engineering (BUBBL)
  • TotalSim Ltd
  • Waters Corporation

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Latest news and blogs

Dr Juan C. Padrino, Research Fellow, University of Warwick

MNF will be present in the upcoming 3rd UK InterPore Conference on Porous Media‚Äč to be held at the University of Warwick, Coventry, UK, on 4 and 5 September 2017.  On the afternoon session of 5 September, Juan C. Padrino will give a talk on multiscale modeling of diffusive transport in complex networks.

Dr Benzi John, Senior Computational Scientist, Daresbury Laboratory

Benzi John (PI) and David Emerson (Co-I) have successfully won about 32, 000 KAU (~ £18,000) frunding from EPSRC to run large-scale simulations on ARCHER. The project titled "High fidelity non-equilibrium DSMC flow simulations at scale using SPARTA" will run for 12 months, starting from August 1st 2017. More information here.

Dr. Duncan Lockerby

Prof. Duncan Lockerby, University of Warwick

It's a pleasure to welcome three new starters to Warwick and the Micro Nano Flows team. Laura Cooper joins us as a post-doctoral researcher, and will be working on multi-phase flow in porous media with James Sprittles. Yixin Zhang and Jacqueline Misfud are in the first weeks of their PhDs. Yixin will be investigating nano film stability (with molecular dynamics) and Jacqui will be researching micro-bubble cavitation (with CFD)  in partnership with Waters Limited. We wish all three the best of luck in their research!

 

Dr Benzi John, Senior Computational Scientist, Daresbury Laboratory

I thought I will mention something about perhaps, the less talked about aspect of droplets, which is its optical properties. Ever since the modern understanding of light and a sound explanation of  the rainbow from an optics point of view (both credited to Sir Isaac Newton in the sevententh century), droplet optics has been studied widely and is today exploited in modern applications. 

An interesting application of this is in lenses and microscopes. In what is called a droplet lens, the natural shape of the droplets is tuned to create a microscope lens. In one of the ways, apparently... the droplet is placed on a glass plate covered with Teflon, to keep the drop round and prevent spreading. An electric current is then applied to the plate to change the droplet shape and by changing the amount of current, one can focus an image through the drop. More recently, researchers at MIT have devised tiny micro-lenses from 'beads of oil mixed in water', which is comparable in size to the width of a human hair. They reconfigure the properties of each droplet to adjust the way they filter and scatter light, similar to adjusting the focus on a microscope. A combination of chemistry and light is used to precisely shape the curvature of the interface between the internal bead and the surrounding droplet. 

More info on this here ......
http://news.mit.edu/2017/microscopes-droplets-0310

Dr. Duncan Lockerby

Prof. Duncan Lockerby, University of Warwick

This is the time of year when I’m reminded of the beauty of fluids. That’s because we’re coming up to the fluid dynamics meeting of the American Physical Society (APS), which organises a headline grabbing “Gallery of Fluid Motion” photo and video competition. If you need convincing of the beauty of fluid dynamics, take a few moments to browse through past winners and entrants, here

An image of some mini vortex rings taken from S. Morris & C.H.K Williamson’s winning poster entry (Cornell)

But why is this competition so popular? Why are fluid flows so easy on the eye? Personally, I think it’s because there is a balance between order and surprise that we see in flow patterns. They are at once intuitive and unpredictable, familiar and bizarre. Like a good film or piece of music – it satisfies us by playing by the rules that we understand, only to surprise us when it breaks them.  Ben Collyer (a past PhD student of the group) would probably say I was complicating things. I recall him saying that flows are pretty, “simply because the fields are two-times continuously differentiable”. He had an ironic sense of humour.

Anyway, with all this in mind, I decided to see if I could make my own ‘fluids art’. I thought it would be fun to be able to create viable fluid fields from photographs (of anything!). The basic technical idea is to convert the intensity of an image (how light or dark it is) into a stream function. A stream function is a simple way to define a 2D velocity field that satisfies the (incompressible) continuity equation (which most fluid flows must). So, this ensures that the flows I generate from an image look physically feasible. I then use a mathematical programming language (Matlab) to create streamlines in the velocity field.

So, like many great artists (!), I decided first to embark on a self portrait:

Hmmm... Well, undeterred by the results, I wanted to see if I could simulate the dissipation of these flow patterns in time (as you would see in the bath, say). I did this be using the velocity field as an initial condition to a numerical solution to the basic fluid equations of motion (here, the 2D unsteady incompressible laminar Navier-Stokes equations). This is what you get (note, the video below is played in reverse, then forwards, then looped).

It was stupid of me to expect that reversing the time would give the impression that my face emerges from the flow dynamics…but it’s sort of interesting to watch. You just can’t beat the real thing, though (watch from 1:30):


So, the conclusion? I’m not going to submit anything to this year’s Gallery of Fluid Motion. But you never know what might be produced in the Micro Nano Flows group for next year…

 
 

 

Chengxi Zhao, PhD Student, University of Warwick

It is widely acknowledged that the flight principle of biological flapping wings (birds, bats and insects) is different from the one of the fixed wings (flight vehicles). For a cruising aeroplane, gases around the wings can be simplified to the steady flow. Lifts come from pressure differences caused by airfoil shapes. However, unsteady characteristics can never be neglected when studying the flapping wings. The flapping motions usually generate vortexes over the upper surfaces of wings. Moreover, the flexibility of biological material makes the problem more difficult because fluid-structure interaction also has to be taken into consideration.

 

The video above shows that honey bees flap their wings up to 250 times a second. It is quite amazing for their small short wings to the 'fat' body off the ground.

 

An interesting idea is that such low Reynolds number flow may exhibit rarefied phenomena at very small scales. Some researchers found that low Reynolds number flows are viscous and compressible, and rarefied effects increase when the Reynolds number decreases (Sun Q. and Boyd I.D., 2004). They also concluded that a flat plate having a thickness ratio of 5% has better aerodynamic performance than conventional streamlined airfoils in rarefied gases. However, it seems that few studies of the topic were carried out after the paper. In my opinion, it is interesting and important to study the rarefied gas effects around the flapping wings to get a deeper understanding of the flight principles of small insects.