Characterization of a hypersonic turbulent boundary layer along a sharp cone with smooth and transverse square−bar roughened wall

Abstract

In the present study, the response of a hypersonic turbulent boundary layer at an inflow of Ma_∞ = 6 and Re_∞ = 16·10⁶ 1/m to a smooth and rough surface along a sharp cone is examined. The model consisted of three segments with exchangeable parts to consider smooth and rough surfaces with a roughness topology of square bar elements with a nominal wavelength of four times the height of the elements. In selected regions of interest, the flow field was measured by particle image velocimetry (PIV) which enabled analysis of mean velocity fields and Reynolds stresses. Van Driest transformed smooth wall mean velocity profiles showed the expected incompressible behavior and compared well to previous investigations. A combination of an integral and fitting approach is discussed to enable inner scaling of the rough wall profiles, which showed the expected shift below the smooth wall profile. The smooth wall turbulence profiles from PIV agreed to artificially filtered DNS in case of the streamwise component. Turbulence profiles above the smooth and rough wall agreed to within measurement accuracies. Additionally, two−point correlations were used to investigate turbulent structures above the smooth and rough wall. Both, length scales and orientations of the correlations, showed high level of agreement between smooth and rough walls, with only differences close to the wall. Furthermore, uniform momentum zones could be identified with similar behavior along both smooth and rough walls. Information from turbulence data support outer layer similarity, whereas mean velocity profiles show an increase in Coles wake parameter for the rough wall data. This might be influenced by transitional roughness effects.