Numerical and experimental investigation of laminar-turbulent boundary layer transition on a blunt generic re-entry capsule

Abstract

Numerical and experimental results on laminar-turbulent transition in the boundary layer of a blunt Apollo-like capsule at 0° and 24° angle of attack are presented. Local stability analyses have been performed and a measurement campaign in the Hypersonic Ludwieg tube Braunschweig at a Mach number of 5.9 was carried out. Infrared thermography showed laminar and transitional surface heating in the unit Reynolds number range of Re_infinity = 6x10^6 /m to Re_infinity = 20x10^6 /m at a surface mean roughness of Ra = 10 micrometer, whereas for a mean roughness of Ra = 0.5 My micrometer no indications for a transitional boundary layer was noted. PCB and Kulite sensors used to measure pressure fluctuations inside the boundary layer do not show any peaks in the frequency spectra which might be related to boundary layer disturbances. The only relevant peak in the spectra does not change with unit Reynolds number and is currently attributed to a bow shock oscillation. Consistent with the experimental findings, the modal instability analysis does not provide any modal boundary layer disturbance growth at windtunnel conditions. Therefore, a scaling ansatz for the laminar boundary layer is introduced and evaluated in order to estimate the unit Reynolds numbers required for the onset of modal disturbance growth on Apollo-like capsules. Results for both first-mode and cross-flow instability are presented.