EXPERIMENTAL STUDY OF THE CORRELATION BETWEEN OIL DOT VELOCITY AND LOCAL SKIN FRICTION IN FLAT PLATE LAMINAR BOUNDARY LAYER

Oil dots on a solid body within a flow field move under the action of skin friction, gravity, pressure, etc. If the accurate relationship of oil dot velocity and local skin friction is obtained, we can easily measure local skin frictions of any type of surface of body including propeller blades and membrane wings whose skin frictions are difficult to be measured by conventional methods. The paper studies experimentally the correlation between oil dot velocity and local skin friction of flat plate laminar boundary layer. Movements of oil dots of silicone oil on a flat plate located in a wind tunnel were recorded by VTR camera. Experimental results confirm the linear correlation of oil dot velocity and local skin friction for each oil dot, but the correlation is much different between the oil dots. The difference is considered to be a result from the initial conditions of oil dots, so it is concluded that it is possible to measure skin friction by tracking oil dot movements.