Wall-shear-stress and laminarisation in accelerated turbulent compressible boundary-layers

Abstract

Turbulent-laminar transition in compressible, steeply-accelerated, adiabatic, turbulent boundary layers on a smooth wall was investigated experimentally in the ranges of Mach and Reynold's numbers typical of nozzles used in propulsive devices. Correlation of the present and previously published data suggests that the transition of such a shear layer may be predicted by consideration of its trajectory on a plane having an acceleration parameter K and a Reynold's number R [sigma] 2 as coordinates. An ab initio design method has been developed, based on these findings, which will ensure laminar flow before and at the throat of a sufficiently small nozzle operating at sufficiently small total pressure. A new type of surface-pilot was developed and calibrated and used to measure wall shear stresses in both transitional and non transitional flows. Decrease of wall shear-stress in lamina rising flows was found. General-purpose computer programs for data-reduction, surface-pilot calibration and interpretation and boundary layer development predictions were developed.