THE ROLE OF THE SHEAR LAYER IN SHOCK-WAVE/TURBULENT-BOUNDARY-LAYER INTERACTION: AXISYMMETRIC SEPARATION STUDIES

Abstract

This thesis presents an experimental investigation into the unsteady mechanisms of high-speed turbulent boundary-layer separation. A range of axisymmetric shock-wave/turbulent-boundary layer interactions is considered and fast-response wall-pressure measurements are obtained to document the resulting fluctuation spectra at high spatial/spectral resolution. The first phase of the programme comprises a detailed characterisation of a large-scale step-induced separation and identifies the dominant influence of the separated shear layer, developing between the inner recirculation and outer high-speed flow, leading to a shift from high- to mid-frequencies as eddies grow over the separation length. Subsequent studies then involve a dedicated characterisation of the shear layer's effect for a variety of step configurations across different separation scales and flow conditions, sustaining its role as the primary driver of the low-frequency bubble breathing mechanism. The final stages eventually extend the analysis to broader axisymmetric ramp interactions to further characterise the entrainment-recharge dynamics associated to interaction low-frequency unsteadiness.