Junior Research Fellow in Engineering Science

Chris Nicholls

  • My research focuses on understanding and controlling fluidic devices, fluid valves with no moving parts that have applications in aerospace.
  • The students at Oxford are bright and enthusiastic about their subject. I learn a lot about engineering from tutoring them!
  • I recently discovered that vortical structures (eddies) in an acoustically-excited fluid shear layer behave in an analogous way to discrete samples in a digital system. The Nyquist-Shannon Sampling Theorem – something that 2nd year engineers learn about – therefore applies, which is an interesting link between two very different fields.

Profile

I am a Junior Research Fellow at Trinity College and conduct research at the Oxford Thermofluids Institute in the Active Flow Control group. I studied engineering as an undergraduate at Hertford College, Oxford, then moved to Lincoln College for my DPhil in active flow control. I am interested in thinking about fluid systems through the lens of signal processing and control theory. This perspective yields new insights in a subject that is traditionally studied in the context of fluid mechanics only. I find it particularly rewarding when the behaviour of a fluid mechanical system mimics an idea in information engineering. Uncovering links between different fields of research is a means of bettering our understanding of the systems that we study.

Research

My work is focused on fluidic devices. These are valves with no moving parts that have great potential in controlling fluid flows in aircraft – from controlling aerodynamics, to active management of engine cooling, to modulating the supply of hydrogen for flame stability. My recent research has focused on developing a new kind of fluidic device that produces an oscillating fluid jet. The oscillating frequency can be influenced via acoustic excitation of the flow, which makes it possible to lock the frequency and timing of the jet onto some reference signal, for example the passing of flow structures over a wing or the passing of blades in a gas turbine.

Selected Publications

C. J. Nicholls, K. Chakravarthy, B. M. T. Tang, B. Williams & M. Bacic, 'On the Nyquist-Shannon Sampling Theorem and acoustically-modulated jet shear layers', Physics of Fluids, 2022, 34(11):115106

C. J. Nicholls, K. Chakravarthy, B. M. T. Tang, B. Williams & M. Bacic, 'Shear layer response to overmodulated acoustic perturbations', Physics of Fluids, 2023, 35(1):015113

C. J. Nicholls & M. Bacic, 'Fluidic oscillator with active phase control', AIAA Journal, 2023, 61(5):1973-1985

C. J. Nicholls & M. Bacic, 'Closed-loop control of a piezo-fluidic amplifier', AIAA Journal, 2020, 58(6):2414-2427

C. J. Nicholls, B. M. T. Tang, J. Turner & M. Bacic, 'Novel operating mode of a fluidic oscillator', ASME Journal of Fluids Engineering, 2022, 144(7):071501

Subjects
Engineering Science
Dr Nicholls
christopher.nicholls@eng.ox.ac.uk