Development of the oil film method of skin friction measurement for curved and free oriented surfaces

A further development of the skin friction measurement technique for free oriented and curved surfaces is described.A theoretical basis and experimental results of using the diffuse lighting to obtain equal thickness fringe patterns of a thin oil film are presented.A possibility of automatic detection of the surface streamline position by analysing the oil visualisation images is discussed.The results obtained show a possibility of using the oil film method for complicated 3D flows.