EXPERIMENTAL-ANALYSIS OF THE TURBULENT SHEAR STRESSES FOR DISTORTED SUPERSONIC BOUNDARY-LAYERS

An experimental analysis of the turbulent shear stresses for a superso nic boundary lay er distorted by streamline curvature-induced pressure gradients was performed using laser Doppler velocimetry, Four pressur e-gradient flows were examined: a nominally zero-pressure-gradient cas e (M = 2.8, Re-theta = 1.1 x 10(4), beta = 0.02); a favorable-pressure gradient (M = 2.9, Re-theta = 1.5 x 10(4), beta = -0.5); an adverse-p ressure gradient (M = 2.7, Re-theta = 1.2 x 10(4), beta = 0.9); and a successive-pressure gradient (M = 2.5, Re-theta = 1.2 x 10(4), beta = -1.0, following a region of beta = 0.9). For the favorable-pressure gr adient, the turbulent shear-stress levels across the boundary layer de creased by 70-100%, as compared to the zero-pressure-gradient boundary layer, Far the adverse-pressure gradient, a 70-100% increase was obse rved. For the combined-pressure gradient, the shear stresses returned to values similar to the zero-pressure-gradient flow. A new pressure g radient parameter was found to correlate well with the peak sheer-stre ss amplification, It was also postulated that the shear-stress amplifi cations were in part the result of the nonuniform hulk dilatation/comp ression and streamline divergence/convergence, implying a forcing phen omena that influenced the statistical <(u'v')over bar> correlation, Th e combined-pressure-gradient flow demonstrated that the turbulent stru cture adjusts relatively rapidly to the distortion, Numerical simulati ons of the mean velocity obtained with a kappa-omega turbulence model were found to agree very well with the present data, With the exceptio n of the zero-pressure-gradient flow, the magnitudes of the turbulent shear stresses were not accurately reproduced; however, correct trends were predicted.