Observations of boundary-layer wind-tunnel flow over isolated ridges of varying steepness and roughness

Boundary-layer wind-tunnel flow is measured over isolated ridges of varying steepness and roughness. The steepness/roughness parameter space is chosen to produce flows that range from fully attached to strongly separated. Measurements show that maximum speedup at the hill crest is significantly lower than predicted by linear theory and that recovery in the lee of the hill is much slower for strongly separated flow over steep terrain. The measurements also show that behaviour of the mean and turbulent components of the flow on the downwind side of the ridge is fundamentally different between separated and non-separated flows. This suggests the dominance of much increased turbulence time and length scales in the lee of the hill in association with a production mechanism that scales with the hill length rather than the proximity to the surface as on the windward side of the hill crest.