Optical skin friction measurements in the short-duration Ludwieg tube facility

The utilization of image acquisition, image processing and skin friction computations has been developed to support skin friction measurements at the Ludwieg-tube facility at DLR. Verification of the oil-film-interferometry technique with analytical tests at different flows with given shear stress distributions showed its advantages and handicaps for skin friction measurements in 3D gradient flows. The abilities of the thin oil film technique with its application in a short duration wind tunnel are demonstrated on some 2D and 3D shock wave / turbulent boundary layer interaction flows.