Project Report

The goal of the research conducted was to gain insight into the effect of surface roughness on the flow over aircraft or other vehicles in order to leverage this knowledge to develop new methods of flow control and perhaps find a way to further decrease vehicle drag that would lead to improved vehicle performance, reduced fuel consumption, and reduced emissions overall. The design of the rough surface studied was inspired by the scales that cover the body of the sailfish, one of the fastest moving sea animals that can reach speeds up to 110km/hr. It was hoped that since the sailfish can travel at such speeds that perhaps its scale pattern acts to reduce drag and conserve energy, much like the drag reducing properties of shark's skin. Work was performed at Seoul National University in South Korea in the lab of Professor Haecheon Choi who specializes in bio-mimetic engineering and who had previously studied the effects of the sailfish scale pattern on flow over the surface. The rough surface in the current set of experiments differed from previous work in that the roughness elements had a large spacing in the direction of the flow, extended further from the surface, and generally mimicked the relative size of the sailfish's scales at its maximum speed where drag reduction would be most critical. In order to test the effects of the roughness on the flow, wind tunnel experiments were performed over a smooth, flat reference surface as well as a surface covered in the proposed roughness pattern. Both the drag on the surfaces as well as the fluid velocity in the immediate vicinity of the surface were measured. While no drag reduction was found compared to the smooth reference case, a very large change in the structure of the flow was noted. This is remarkable as the roughness was not that large (0.8mm tall or about 40 times smaller than the boundary layer, the region of the flow affected by the presence of the wall) and was sparsely spaced. Such a large change in the flow over the surface with a minimal increase in drag may make such a surface useful as a flow control device for aircraft. The actuation of such a surface could be used to manipulate the flow and thus maneuver the vehicle with the advantage that the very small actuation height would require less energy input than conventional control surfaces such as flaps and slats.

National Science Foundation (NSF)
Office of International and Integrative Activities (IIA)
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Carter Kimsey
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Lehew Jeffrey A
United States
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