Skin Friction Drag Reduction in Turbulent Boundary Layer Conditions over Riblet Surfaces

摘要

Wind tunnel tests and flight tests have been performed to evaluate riblets for skin friction drag reduction at turbulent boundary layer conditions. The riblet with fine grooves is made from aviation paints. The skin friction coefficients were calculated from momentum thicknesses from velocity profiles over smooth surface and riblet surfaces measured by pitot rakes on flat plates in the wind tunnel tests. Additionally, measurement of streamwise turbulence intensity was implemented using a hot-wire anemometry. The results of mean velocity in flight tests indicate that a paint-riblet worked effectively. It was found that the drag reduction rate obtained at different wind tunnels is approximately 5 - 6 % and the streamwise turbulence intensity is decreased by the riblet for the case of drag decreasing. The drag reduction rates obtained in the wind tunnel tests are qualitatively consistent with those obtained by the direct numerical simulation over a wide range of 5% though the magnitudes of Reynolds number based on momentum thicknesses (Re_θ) obtained from those methods differ.