Open channel boundary layer relaxation behind a forward facing step at lowReynolds numbers

This paper reports laser-Doppler anemometer measurements of mean velocity a nd turbulence statistics upstream and downstream of a 3-mm forward facing s tep in a shallow open channel flow. The Reynolds numbers based on the momen tum thickness (theta) of the approaching upstream flow, and step height (h) are in the range 1010 less than or equal to Re (0) less than or equal to 2 240 960 less than or equal to Re (h) less than or equal to 1890, respective ly. Measurements are obtained at 50 step heights upstream of the leading ed ge of the step and 1 less than or equal to x/h less than or equal to 162 do wnstream of the step. The results show that the overlap region develops mor e slowly than the inner and outer regions. The mean field recovers at x/h = 50, Distributions of the turbulence intensity tend to become selfsimilar fo r x/h > 100 but the profiles do not necessarily collapse onto the upstream profiles.