Dr Richard Hodgkinson will be joining our Department in April following his successful application for a National Fellowship in Fluid Dynamics (NFFDy). His “S.E.C.R.E.T. : Shear Extension Combined Rheology Experimental Techniques” project will expand a new line of research he started into better understanding complex rheological flows, pertinent to a wide range of situations. UK Academics from Leeds, Liverpool, UCL and Hull will be collaborating with him on his project.
The NFFDy fellowship application was highly competitive with 230 applications to the scheme. Richard was top of the rankings going into the interview stage. Richard joins a close-knit community of 11 successful fellows for the next 3-4 years, under a scheme aimed at addressing the emerging need for advanced training in fluid dynamics. It also provides a route for the most talented PhD graduates in fluid dynamics to stay in this research area and contribute to the advancement of the field in the UK. It covers computational fluid dynamics, laboratory experiments and real-world observational measurements, recognising that fluid dynamics contributes to strategic objectives; objectives ranging from net zero to productivity and resilience.
“I am thrilled to have been awarded this fellowship. It gives me a unique opportunity to lay groundwork in a new field I ventured into during my PhD, and I am honoured that the scientific community concurs with the importance of the research.
I have already worked closely with academics in the department, and I am very much looking forward to where joining the team will lead. Additionally, working with the medical school to use their MRI facilities to enable the experiments is particularly exciting – both the collaboration and the cross-discipline use of state-of-the-art instruments. I’ve investigated applying MRI to my work since my PhD, but to be here, now, with the opportunity in front of me is fantastic.”
Project summary
Are you familiar with piping icing onto cakes? Would you be surprised to know that our understanding of many of the flow processes taking place whilst you lay down beads are not actually fully understood?
Wherever a fluid is "strained" - slid, squashed, or changed in shape, it responds with a force, or "stress". Studying fluid response to straining is known as "rheology". These forces influence how the rest of the fluid nearby moves, making it vital information to be able to computationally model fluid flow problems: models that inform processing molten plastic into everyday objects, or our understanding of how a spider spins its’ silk. Colloquially, rheology describes how "thick" a fluid is, but fluids can have hugely varying behaviours, all dependent on microscopic interactions occurring within them.
The flow and straining occurring through a piping nozzle is quite complicated:
- Near the nozzle walls, icing is mainly undergoing a "shearing" flow, where fluid layers slide over one another - this flow type is well understood and measurable in a lab.
- Near the centre, the fluid is experiencing "extension", where fluid packets are stretched in the flow direction and squashed in other directions. The nozzle tapering causes this. This extensional flow is less well understood or measureable, but in the last 50 years our understanding has improved, mainly because of the plastics industry (e.g. extruding plastic profiles).
- Between the location of the wall and the centre of the flow, simultaneous shear and extension exists – we call this a "kinematically mixed" flow. Not stirred, but mixed as in more than one type of straining being present.
Until now there hasn't been a way to unambiguously isolate and measure the separate stresses in the latter region. Stresses depend, via microscopic interactions in the fluid, on both shear and extension together – e.g. particles or long chain-like polymer molecules getting slid, unfurled, stretched and/or rotated in the flow and how they subsequently interact with one another.
The same way that icing holds its’ shape, resisting flow when deposited, is shared by applications such as depositing solder paste for manufacturing electronic devices and 3D printing cement to build futuristic homes. This makes the understanding of fluid rheology and how it is affected by the process critical. These were all examples of “suspensions”. Richard’s PhD work showed that there is complex behavioural coupling from shear and extension for a polymer solution using an optical approach. Now, the opportunity to apply MRI (Magnetic Resonance Imaging – the scanner being used is the one in the photo above) to the experimental technique he developed means a wide variety of systems can now be probed. This includes suspensions which are opaque, but also covers engineered systems for specific interactions with behaviours unique unto themselves. One material processing example that this work will impact is better understanding the flow behaviour of carbon fibre, also a suspension when in solution. Aside from finding new behaviours, integration of a “round-table” of academics will lay a foundation for the modelling community to develop new, improved fluid models. These models will allow more accurate process design for new materials and consequently reduce process troubleshooting; key to improving the cost and sustainability of consumer products.