Image Measurement of Wall Friction Using Oil Film

A new technique for wall friction measurement, non contact and instantaneous measurement, is developed. The method is a kind of the so-called image measurement using oil flow on wall and image analysis technique. Oil flow owing to wall friction is very small and also strongly depends on way of painting. The possibility of the measurement is examined in a flat plate flow.It is possible to measure the wall friction, if small displacement of oil can be measured. The spatio-temporal derivative method of image analysis is effective for this measurement. The ordinary oil film method for circulating water channel, based machine oil and liquid paraffin with carbon black powder, is employed here from the practical view point.The present method was applied to a juncture flow around a circular cylinder on the flat plate, the so-called horseshoe vortex, in which it is impossible to use any probe for wall friction measurement. The limiting streamlines on stern hull are also measured. The result is agree with the visualized one with milk painting method.