Non-osculating Surface Skin Friction Measurement Method with Use of Laser

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A method of accurate non-osculating measurement of surface skin friction with the principle obtaining a thickness of silicon oil poured on the body surface by utilizing the fact that the oil thick-ness is varied by flow shearing stress is proposed. At first a method using dual-beam laser is used, where interaction between a laser beam which is reflected on the oil surface and that transferred within the oil is received by the light fiber fixed on the body surface. Secondly a method utilizing luminescent paint is adopted. This method is on the principle that the luminescent paint contained in the oil emits radiation whose intensity is proportional to oil thickness. These two methods were applied for skin friction measurement on flat plates with and without angle of attack, airfoil without angle of attack and a flat plate with laminar flow control (boundary layer suction) through error estimation. It is shown that these methods have advantage of relatively simple structure and possibility of quick and low cost measurement. The way of combining the merits of these two methods is discussed and the perspectives of non-osculating skin friction measurement method is considered through recommendations of further application to practical problems and modification of the technique.