Mechanics of Sheet Flow under Simulated Rainfall

Friction factors are presented for spatially varied sheet flow with rainfall on a hydraulically smooth surface as obtained from both surface profile and hot film surface probe measurements. The results are presented in the form f = C/R, in which C increases with rainfall intensity and surface slope. A two-part velocity profile mathematical model based on von Karman's similarity hypothesis is presented and correlated with hot film measurements. Relative longitudinal turbulence intensity profiles with rainfall are characterized by a sharp increase in relative intensity near the surface and a general increase throughout the depth with increasing rainfall. Turbulent energy spectral analyses indicate that the rainfall causes a shift of the energy content to higher frequencies than for the case of uniform flow at the same Reynolds number.