Abstract
Friction and pressure drags acting on two- and three-dimensional wavy walls are investigated using a three-dimensional direct numerical simulation (DNS). Two conventional methods for estimating the friction velocity from the log-law of the mean velocity and a peak value of the Reynolds stress were also examined applying the result of DNS. The results show that the ratio of the friction drag to the pressure drag is 0.86 and 2.9 for two-and three-dimensional wavy walls, respectively. Both conventional methods overestimate the friction velocity at about 10% for a two-dimensional wavy wall but they give good accuracy for a three-dimensional wavy wall.
