Characterization of a Hypersonic Turbulent Boundary Layer along a Sharp Cone with Smooth and Rough Walls

Abstract

This work presents experimental studies on hypersonic turbulent boundary layers along smooth and rough walls, performed in the Hypersonic Test Section H2K of the German Aerospace Center in Cologne. The generic model for the experiments is a sharp cone consisting of three segments with exchangeable parts to consider smooth and rough surfaces. One segment consists of a technical roughness topology with square bar elements with a nominal wavelength of four times the height of the elements. Another segment consists of sand grain type roughness utilizing Carborundum grains. The boundary layer is probed with a Pitot pressure rake and Particle Image Velocimetry (PIV). The analysis encompasses the mean and turbulent features of the velocity distribution and large-scale coherent structures of the turbulent boundary layer. Further, the convective heat flux is deduced via infrared thermography and local sensors. Additionally, Schlieren images and surface pressure data is used to gain general information about the flow field along the cone model. The interpretation of the experimental data is supported by analytical correlations and simulations conducted with a boundary layer code and computation fluid dynamics code TAU. In case of the boundary layer code, a modified roughness model was used to compare to rough wall experiments.