Combined Experimental and Numerical Investigation of a Hypersonic Turbulent Boundary Layer by Means of FLDI and Large-Eddy Simulations

Abstract

This work investigates a hypersonic turbulent boundary layer over a straight cone with cold walls at M = 7.4 and Rem = 4.2 · 10^6 m^−1, in terms of density fluctuations away from the wall and convection velocity of density disturbances. Experimental data is collected in a shock tunnel using a multi-foci Focused Laser Differential Interferometer (FLDI) to probe the boundary layer at several different heights from the cone wall. In addition, a high-fidelity, time-resolved Large-Eddy Simulation (LES) of the conical flowfield under the experimentally observed free stream conditions is calculated. The experimentally measured convection velocity of density disturbances is verified to follow literature data of pressure disturbances. The spectral distributions evidence the presence of regions with well-defined power laws. As an alternative to complex methodologies to compensate the frequency roll-off caused by the FLDI spatial filtering, a computational FLDI (cFLDI) is calculated on the numerical solution for direct comparison with experiments. Frequency bounds of 160 kHz < f < 1 MHz are evaluated in consideration for constraining conditions of both experimental and numerical data. Within these limits, the direct comparisons yield reasonable agreement. It is also verified that in the present case the cFLDI algorithm may be replaced with a simple line integral on the numerical solution.