Experimental Investigation on Effects of Surface Roughness Geometry Affecting to Flow Resistance

Experimental investigation on effects of surface roughness geometry affecting to flow resistance has been carried out. The concentric cylinder device composed of outer cylinder and inner test cylinder was employed to the experiment. We prepared 24 different roughness models having various skewness of roughness profile as test inner cylinders. Surface of test cylinder has ridge and valley roughness whose shapes are isosceles right triangle V-shape. These ridge and valley are arranged at equal intervals. Therefore, RMS roughness of the surface and skewness of the surface roughness profile can be evaluated. In the experiment, inner cylinder is rotated but outer cylinder is stationary, torque of rotating inner cylinder was measured. Based on the torque measurement, we investigated the effect of skweness of the surface roughness on flow resistance. As a result, when the roughness profile has Gaussian distribution (skewness = 0), friction coefficient increases with increasing RMS roughness. Moreover, friction coefficient also increases with increasing skewness of surface roughness under same RMS roughness. In order to predict the friction coefficient from the geometric information of the surface, we estimated the equivalent sand grain roughness from surface roughness parameters. Results showed that it was clarified the relation among skewness of roughness profile, equivalent sand grain roughness and the root mean square of surface roughness.