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 were demonstrated on some examples. The comparison of experimental results obtained by different optical skin friction methods demonstrated good agreement.