EXPERIMENTAL INVESTIGATION OF THE EFFECTS OF SURFACE ROUGHNESS ON COMPRESSIBLE TURBULENT BOUNDARY LAYER SKIN FRICTION AND HEAT TRANSFER

Abstract : An experimental investigation was carried out to determine the effects of surface roughness on the turbulent boundary layer skin friction and heat transfer rates in air at a Mach number of 4.93. Four flat plate model configurations were tested. Simultaneous measurements of the local skin friction and heat transfer were made. The results of these measurements and of boundary layer pressure surveys are presented. Agreement of the smooth plate results with accepted theories acts to substantiate the results of measurements using the rough-surfaced models. A method is given to determine the equivalent incompressible sand-grain roughness of a surface based on experimental knowledge of the skin friction in compressible flow. In addition, a method to account for heat transfer effects in the calculation of skin friction coefficients for rough plates is suggested. Using the experimental results, the validity of the Reynolds analogy between heat transfer and skin friction is examined. A method to determine the Reynolds number based on the length of the turbulent boundary layer from measurements of the skin friction and momentum thickness for smooth or rough flat plates is also given.