Measurements of Turbulent Friction on a Smooth Flat Plate in Supersonic Flow

Abstract

Direct measurements of supersonic local skin friction, using the floating-element technique, are presented for Mach Numbers from 2.0 to 4.5 and Reynolds Numbers from 3 X 10^5 to 9 X 10^6. Turbulent flow and transition are emphasized, although some measurements in the laminar regime are included. The observed effect of compressibility is to reduce the magnitude of turbulent skin friction by a factor of two at a Mach Number of 4.5 and a Reynolds number of about 10^7. The boundary-layer momentum-integral equation for constant pressure is verified within a few per cent by two experimental methods. Typical static pressure measurements are presented to show that transition can be detected by observing disturbances in pressure associated with changes in displacement thickness of the boundary layer. It is found that the turbulent boundary layer cannot be defined experimentally for values of u_1 θ/v_1 less than about 2,000, where θ is the momentum thickness. For larger values of u_1 θ/v_1, there is a unique relationship between local friction coefficient and momentum-thickness Reynolds Number at a fixed Mach Number. The Appendix compares the present measurements at M = 2.5 with experimental data from other sources.