DAMPING OF SURFACE PRESSURE-FLUCTUATIONS IN HYPERSONIC TURBULENT-FLOWPAST EXPANSION CORNERS

Surface pressure fluctuations of Mach 8 turbulent flow past a 2.5- and a 4.25-deg expansion corner maintained a Gaussian distribution but we re severely attenuated by the expansion process. The pressure fluctuat ions did not recover to those of an equilibrium turbulent flow even th ough the mean pressures reached downstream inviscid values in four to six boundary-layer thicknesses. The fluctuations were convected with a velocity comparable to that on a flat plate, and they maintained thei r identities longer for the stronger expansion. The damping of pressur e fluctuations at hypersonic Mach numbers, even by small corner angles , may be exploited in fatigue design.