Experimental Investigation of a Supersonic Boundary Layer Including Favorable Pressure Gradient Effects

This study used advanced laser Doppler velocimetry techniques to measure the turbulence intensities and Reynolds shear stresses in Mach 2.8 turbulent flat plate and Mach 2.9 favorable pressure gradient (FPG) boundary layers. The FPG was generated using a convex curved wall and had a strength of ß = 0.1, where ß is Clauser\u27s equilibrium parameter. The maximum magnitude of the \u27extra\u27 strain rates normalized by the main strain rates was 0.1, which meant the FPG was considered to be a strong pressure gradient. The fiat plate results indicated that the LDV procedures used in this experiment prevented angular biasing of the velocity measurements reported in the literature. Analysis of the LDV system settings also showed that this biasing, which has been attributed in the past to the angular alignment of the lasers, may have actually been caused, at least in part, by the choice of record interval used during data collection. Measurements in the FPG test section demonstrated that the stabilizing effect of the FPG reduced the turbulence intensities below the location y/δ ≤ 0.5. Near the wall, the u-turbulence intensity was found to be reduced to 70% of the flat-plate value. In addition, the FPG reduced the magnitude of the incompressible Reynolds shear stresses (-pu\u27v\u27) by approximately 75%. Comparison of the LDV data to hot-wire data collected in the same facilities showed that the assumption of p\u27 = 0, used in the reduction of the hot-wire data, was valid in the fiat plate region but not the FPG region. The increase in the magnitude of p\u27 was likely due to the streamline curvature associated with the generation of the FPG and the resulting pressure difference across the boundary layer