DIRECT NUMERICAL SIMULATION OF OPEN-CHANNEL FLOW AT LOW-FROUDE NUMBER BASED ON SMALL-AMPLITUDE WAVE THEORY

A directn umericals imulationo f a fully-developed turbulent flow in a two-dimensional open channel has been conducted. The effects of the instantaneously deforming free surface and the fluctuation of the vertical velocity component at the free surface are taken into account by applying the small-amplitude wave theory. The results obtained at two subcritical Froude numbers are compared with those conducted for the closed-channel flow and those for the open-channel flow with free-slipa pproximation for the free surface. Generally, the effects of the motion of the free surface on such quantities as the mean velocity and Reynolds stress distributions and their transports are found to be small except for quantities involving the vertical fluctuation near the surface. The effects on the eddy viscosity coefficient were the most significant and over a large region.