Method of predicting frictional resistance of rough surface and surface performance evaluation apparatus

摘要

[Object] The invention provides a method which predicts a ratio of the increase in frictional resistance of a rough surface in a simple manner, quickly and without variations in predicted results among individuals. [Solution] The method for predicting the frictional resistance of a rough surface having a variation in roughness wavelength, and being in contact with a fluid flowing at varied velocities includes evaluating the total projected area A of all prominent peaks standing out above the viscous sublayer thickness per unit area (hereinafter, written as the "prominent peak projected area A"), and calculating the friction increase ratio FIR (%) using Equation (1) below or the frictional resistance increase ”Ä using Equation (2) below. FIR % = C × A ” Ä = C r 1 2 Á AV 2 (In Equation (1), the coefficient C is a constant dependent on the prominent peak projected area A and is determined by performing a frictional resistance test beforehand in which the frictional resistance is measured with respect to a plurality of rough surfaces differing in the degree of roughness while changing the flow velocity V and the friction increase ratios FIR (%) of the rough surfaces are calculated wherein the friction increase ratios FIR (%) are percentages of the difference Ä r - Ä 0 between the frictional resistance Ä r of the rough surface and the frictional resistance Ä 0 of a smooth surface, divided by Ä 0 . In Equation (2), the coefficient C r is a constant dependent on the fluid density Á, the prominent peak projected area A and the flow velocity V and is determined from the relation of Equation (2) using values of frictional resistance increase ”Ä obtained beforehand by a frictional resistance test in which the frictional resistance is measured with respect to a plurality of rough surfaces differing in the degree of roughness while changing the flow velocity V wherein the values of frictional resistance increase ”Ä are the differences Ä r - Ä 0 between the frictional resistance Ä r of the rough surface and the frictional resistance Ä 0 of a smooth surface.)