Open Channel Boundary Layer Relaxation Behind a Forward Facing Step at Low Reynolds Numbers

Abstract

This paper reports laser-Doppler anemometer measurements of mean velocity and turbulence statistics upstream and downstream of a 3-mm forward facing step in a shallow open channel flow. The Reynolds numbers based on the momentum thickness (θ) of the approaching upstream flow and step height (h) are in the range 1010≤Reθ≤2240 and 960≤Reh≤1890, respectively. Measurements are obtained at 50 step heights upstream of the leading edge of the step and 1≤x/h≤162 downstream of the step. The results show that the overlap region develops more slowly than the inner and outer regions. The mean field recovers at x/h=50. Distributions of the turbulence intensity tend to become self-similar for x/h>100 but the profiles do not necessarily collapse onto the upstream profiles.