Neutral flow over a series of rough hills: A laboratory experiment

This paper presents laboratory experiments of aerodynamically fully rough, neutral flow over a series of sinusoidal hills. Two sets of hills, with maximum gradients (slopes) of 0.2 (10 degrees) and 0.4 (20 degrees), were considered. The flow remained attached in the former case while separation occurred in the latter. Characteristics of the mean flow and turbulence statistics are discussed and compared with profiles over a flat surface covered with the same roughness as the hills. Comparisons are made with linear theory predictions for the flow in the inner region and aloft. Accurate measurements of the surface pressure were also made, enabling the comparison between the measured pressure drag and predictions from theoretical and computational work with different turbulent closure schemes. Organised secondary flow in the spanwise direction, observed previously in both experimental and computational studies, was also observed here over the small hills.