Accurate skin friction measurement over 3D surfaces via a simplified photogrammetry procedure in oil-film interferometry

In this talk, we present the results of our recent study [1], where a simplified procedure of implementing photogrammetry in oil film interferometry (OFI) is developed for accurate skin friction measurements over a three-dimensional (3D) bump geometry. The technique allows photogrammetry application on any 3D surfaces without a priori knowledge of model geometry or conducting a tedious process of model geometry reconstruction via reference points. Our simplified method is based on camera calibration algorithms and a flexible small checkerboard. The method was first validated with the Clauser method over a flat surface in a canonical turbulent boundary layer. Then the method was applied to obtain the skin friction distribution for turbulent flow over 3D Gaussian bump geometry, which exhibits smooth body flow separation. Our method is suggested to complement and validate simulation studies to examine key phenomena in the flow field over complex geometries.