Correction of Wind Tunnel Test Data for Additional Roughness Drag

Abstract

A method to correct wind tunnel test data for the additional drag caused by roughness elements in a fully turbulent boundary layer is proposed using drag polar curves obtained from wind-tunnel tests. It is assumed that boundary layer over a wind tunnel model is fully turbulent at high absolute angle of attack both with and without roughness elements from the results of measurements using Preston tubes, and that the additional drag due to the roughness elements is constant over the entire range of the angle of attack. The additional roughness drag is estimated using the axial force data obtained from internal balances. The method proposed was validated using the data from wind tunnel tests with the same Mach number with two models obtained from two different wind tunnels. The differences in the values of minimum drag coefficient obtained from the two wind tunnels tests corrected by this method were smaller than those corrected using a conventional method, and they were well within the uncertainties in terms of the drag coefficient. Furthermore, the additional roughness drag can be estimated by this method when applying wind tunnel data obtained using only a single roughness height.