Laurent M. LE PAGE, Andrew CERUZZI, Thomas L. J. BRAIN, Alexander J. RIELEY, Tristan J. CRUMPTON, James C. ROBSON, Matthew ECKOLD, Matthew MCGILVRAY

DOI Number: 10.82241/ceas-hisst-2024-290

Conference number: HiSST-2024-290

This paper presents a preliminary study of hypersonic boundary layer phenomena resulting from the energy deposition of an ultrafast laser pulse in proximity to the tip of a 7° half-angle axisymmetric cone within the Oxford High Density Tunnel (HDT) facility. An ultrafast Ti:Sapphire laser was integrated into the facility’s systems, providing temporally precise and synchronous delivery of a single tightly focussed laser pulse to the target location in the HDT test section. This investigation independently assessed the variation of the freestream unit Reynolds number (Reunit,∞) on the disturbed boundary layer for laminar to turbulent conditions bound by the extrema unit Reynolds numbers 5.7 and 24.1 ±
0.9 × 106/m, while keeping laser settings constant. For all test conditions, the boundary layer state was characterised using high-speed schlieren imaging at 1 MHz for visualising the flow field, focussed laser differential interferometry (FLDI) to assess small density fluctuations, and surface-mounted high-frequency bandwidth pressure transducers (PCBs 132A31 and 132B32). Flow features associated with the energy deposition in the boundary layer, included the formation of a spherical shock wave that expanded radially and decayed, an elliptical high-temperature ‘hot spot’ region, and a trailing turbulent wake. The hot spot and turbulent wake density gradients increased linearly with unit Reynolds number, suggesting a relation to the local mean density or pressure. Normalising these values by mean density gave an estimate of turbulence intensity, which appeared independent of unit Reynolds number. The size of the hot spot decreased with unit Reynolds number, which is hypothesised to be caused by the higher mean pressure compressing the hot spot. The increasing instability of the boundary layer with unit Reynolds number led to longer duration turbulent wakes before the laminar boundary layer re-establishes.

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In Categories: 1.Events, High-Speed Aerodynamics and Aerothermodynamics, HiSST 2024
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