A Wind tunnel study of turbulent flow over double steep hills

Abstract

The effect of two- and three-dimensional double steep hills on the mean velocity and turbulent characteristics of a boundary-layer were investigated in a wind tunnel. The mean flow and turbulence were measured using split-fiber probes designed for measuring flows with high turbulence and separation. The results were as follows: 1) Profiles of mean velocity and the standard deviation of the fluctuating velocity components above an upwind hill for continues two- and three-dimensional hills were similar to those of the the single hill. 2) The mean velocity data at a downwind hilltop for continues two- and three-dimensional hills had lower values compared to that of upwind hilltop data. However, the standard deviation of fluctuating velocity components on the downwind hilltop data was higher than the values of the upwind hilltop data. 3) The reattachment behind downwind hill for continues two- and three-dimensional hills was smaller than that of the single hill. 4) Velocity variance on downwind hilltop was greatly influenced by the distance between the double hill. The perturbation increased with the distance and the maximum perturbation in two-dimensional hills occurred beyond 12-15 hill heights, because of vortex shedding by upwind hill.