Very many congratulations to Sam Shelley, EPSRC CDT in Metamaterials PGR, who recently submitted his PhD thesis titled “The Control of Fluid Flow Using Metamaterials Concepts”. Sam was supervised by Roy Sambles (FRS), Alastair Hibbins and Simon Horsley, and previously published his work on Fluid Mobility over Corrugated Surfaces in the Stokes Regime and on Emergent propagation modes of ferromagnetic swimmers in constrained geometries. In addition, he has presented his work on Flow Control over the past 4 years through posters and talks at national and international conferences, such as the Defence and Security Doctoral Symposiums and the APS Division of Fluid Dynamics meetings. During a research stay with the CREAte group at Virginia Tech (Blackburg, Virginia, US) he enjoyed in particular the opportunity to exchange research interests, support their experimental setup and building of collaborations. Sam also shared his passion for research and science with children and adults at public engagement events such as the Sidmouth Science Festival, the Royal Cornwall Show, and the Big Bang Southwest.
We look forward to further close working relationships as he continues his research as a postdoc at the University of Exeter, and wish him good luck for his viva as the final stepping stone towards the PhD.
“The CDT has been a great experience over the past four years. Working as part of a cohort has meant that we have all been able to support each other as we have all been going through similar things. I have made some great friends during my PhD and I hope I get to work with them again.” (Sam Shelley, September 2018)
Thesis abstract
The work presented in this thesis concerns the application of concepts that are widely used in metamaterial research to the control of fluid flow. In particular surface structuring and resonance were investigated.
The initial work focussed on Stokes flow over structured surfaces. The effective boundary conditions that the structuring creates, analogous to the impedance boundary condition encountered in electromagnetism and acoustics, were examined. Exact solutions for the flow and slip length along the grooves of a family of surfaces were derived. These were compared to Finite Element Method (FEM) models and previous work valid for arbitrary structured surfaces, which was based on a perturbation expansion. Good agreement was found for all available surfaces. The previously presented solution was then also compared to results for a sinusoidal surface, finding good agreement for low aspect ratios but diverging at intermediate aspect ratios. Extending the perturbation theory beyond first order was found to improve the agreement.
To explore the concept of resonance in fluid dynamics laminar flow around a circular bluff body with an attached flexible tail was considered, investigating how the resonant behaviour of the elastic tail modified the drag and vortex shedding frequency of the body. The results were compared against the no tail case as well as a rigid tail. For short tail lengths the average drag was reduced compared to both reference cases, whilst the vortex shedding could be either enhanced or reduced. When one of the resonant frequencies of the tail matched the vortex shedding frequency of the body, the resonance motion of the tail resulted in in sharp changes to both the drag and vortex shedding frequency.
In the finally section of the thesis I describe the Particle Image Velocimetry experiments that were set up to verify the resonant flexible tail behaviour. The process by which the initial set up was upgraded is given. Results are shown for a circular bluff body being towed through the fluid. This is then extended to a circular bluff body with an attached rigid tail. Preliminary results for the flexible tail case are then presented.