Hypersonics and High Speed Flows

Hypersonics

Hypersonics is the study of flows that are much faster than the speed of sound, and is important for very high-speed flight of aircraft, and entry of probes into planetary atmospheres.  When vehicles travel at hypersonic speeds, temperature changes are large enough to significantly change the behaviour of the flow compared to lower-speed flight, changing the aerodynamics of vehicles and providing a very challenging flight environment for aerospace systems.  We study these effects using advanced laser-based techniques and high-speed physical to provide a better capability for designing high-speed aerospace systems.  Even using advanced computational techniques, there are still significant uncertainties in predicting the behaviour of vehicles under hypersonic flight conditions.  We use our free-piston shock tunnel facility, T-ADFA, to provide a test bed for the behaviour of model hypersonic vehicles and propulsion systems, and we collaborate with computational experts in Australia and overseas in comparing our experiments with state-of-the art computational simulations.  We also use our capabilities in high-speed flow imaging to investigate transient flow phenomena and interactions between the flow and the vehicle’s structure. The challenges in this field are the very short test times (typically below one millisecond) and the low density of the free stream flow. We have developed special diagnostic techniques that allow us to visualise these flows.

The upper image below shows a comparison between vertical flow velocity component measurements in our facility (upper half of image) and computational models of the same velocity component (lower half of image).  The differences between computations and experiments at these conditions allow us to test our understanding of the fascinating flow processes taking place at these extreme flight conditions.

The second set of images illustrates the aforementioned challenges encountered when observing hypersonic flows – the bottom half shows the flow field when visualised with a conventional schlieren method, while the top half shows the same flow field visualised with a resonantly enhanced shearing interferometry method developed in this group. This technique has allowed us to investigate details of the low-density wake flow behind re-entry vehicles.

comparison between vertical flow velocity component measurements

challenges encountered when observing hypersonic flows

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