Transition Experiment with a Blunt Apollo Shape like Capsule in Hypersonic Ludwieg Tube

Abstract

Experimental and numerical results on laminar-turbulent transition in the boundary layer of a blunt Apollo-like capsule at 0° and 24° angle of attack (AOA) are presented. Infrared thermography was used to observe the transition behavior for varying unit Reynolds number runs (Re∞ = 6e6 /m to Re∞ = 20e6 /m) and for two different surface condition. For the investigated capsule surface with a mean roughness of Ra = 10 μm, transitional surface heating firstly appeared at about Re∞ = 15e6, whereas for a mean roughness of Ra = 0.5 μm no indications for a transitional boundary layer were found at all. PCB and Kulite sensors are used to measure surface pressure fluctuations inside the boundary layer, but did not show any peaks in the frequency spectra which might be related to harmonic boundary layer disturbances. The only relevant peak in the spectra is attributed to bow shock oscillations. Space/time correlations of pressure data indicates low linear correlation of consecutive and crosswise placed sensors and help to characterize the nature of pressure fluctuation.