Dynamics of the shock wave in supersonic air-intake systems

Imperial College London

Commercial high-speed aircraft provide a reduction in flight time and eases air traffic management for the United Kingdom, which plans for 70% more flights over the next three decades. With aviation accounting for 6% of the total greenhouse emissions, achieving the UK's net-zero carbon emissions target also requires increased investments into new aircraft and engine technology, such as hydrogen-powered engines. However, pragmatic hydrogen-powered aero propulsion, offering high-speed and efficiency, faces several challenges. Some of the critical problems that hinder their development are "huge levels of noise and fuel-inefficiency" – both closely associated with a flow phenomenon known as engine "unstart", which is caused by interactions between the flow shock waves and the acoustic waves propagating inside the engine. Engine air-intakes can be made stable to "unstart" by operating at inefficient conditions with significant energy losses. Efficient conditions are generally those susceptible to un-start. This conundrum means that increasing efficiency increases vulnerability to unstart.

With recent advancements in air-breathing rocket engine technology at Reaction Engines Ltd. (UK), the un- start problem is receiving renewed attention. The fellowship benefits from industrial collaboration with Reaction Engines. It aims explicitly at ensuring stable and efficient regimes of operating conditions for the new class of hydrogen-powered engines. This is achieved by developing full-scale models for engine unstart, given an engine design on paper, and identifying conditions leading to un-start. Using a multi-scale approach that combines separate treatments for the different physics at play, for instance, high-fidelity numerical simulations will be used for the high-speed flow and mathematical models for the acoustic wave propagation, leading to models that combine accuracy, computational efficiency, and physical insight. Multi-scale treatments also offer swift parametric sweeps across various flight conditions, compared to conventional fully numerical or experimental procedures.

Successful implementation of the model to the development engine brings us one step closer to efficient and accessible high-speed hydrogen-powered civil aircraft. This mitigates the air-traffic by reducing flight time and meets the emission targets - offering direct industrial and societal impact.