Application of spalding formula in wall friction stress measurement on riblet surface

The mean velocity distributions in turbulent boundary layers of smooth surface and two different riblet surfaces are measured with IFA300 constant-temperature anemometer in low-speed wind tunnel to validate the full development of turbulent boundary laye. Friction velocity and wall friction stress of turbulent boundary layer are obtained with the least-squares fitted curve of the sublayer velocity distribution based on Spalding formula, and virtual origin position of riblet surface can be acquired accurately. Moreover, the momentum loss thicknesses of these three experimental models is also calculated. The results show that the drag reduction effect is obvious in turbulent flows due to the riblet surface with the comparison of the momentum loss thicknesses and wall friction stresses of smooth surface and riblet surface.