Experimental Analysis of the Turbulent Shear Stresses for Distorted Supersonic Boundary Layers

Abstract

An experimental analysis of the turbulent shear stresses for a supersonic boundary layer distorted by streamline curvature-induced pressure gradients was performed using laser Doppler velocimetry. Four pressure-gradient  ows were examined: a nominally zero-pressure-gradient case (M = 2.8, Reu = 1.1 3 10, b = 0.02); a favorable-pressure gradient (M = 2.9, Reu = 1.5 3 10, b = 20.5); an adverse-pressure gradient (M = 2.7, Reu = 1.2 3 10, b = 0.9); and a successive-pressure gradient (M = 2.5, Reu = 1.2 3 10, b = 21.0, following a region of b = 0.9). For the favorable-pressure gradient, the turbulent shearstress levels across the boundary layer decreased by 70 – 100%, as compared to the zero-pressure-gradient boundary layer. For the adverse-pressure gradient, a 70 – 100% increase was observed. For the combinedpressure gradient, the shear stresses returned to values similar to the zero-pressure-gradient  ow. A new pressure gradient parameter was found to correlate well with the peak shear-stress ampliŽ cation. It was also postulated that the shear-stress ampliŽ cations were in part the result of the nonuniform bulk dilatation/compression and streamline divergence/convergence, implying a forcing phenomena that in uenced the statistical correlation. The combined-pressure-gradient  ow demonstrated that the turu9v9 bulent structure adjusts relatively rapidly to the distortion. Numerical simulations of the mean velocity obtained with a k-v turbulence model were found to agree very well with the present data. With the exception of the zero-pressure-gradient  ow, the magnitudes of the turbulent shear stresses were not accurately reproduced; however, correct trends were predicted.