Effect of momentum injection on drag reduction of a barge-like structure

Using a rectangular prism with square cross-section and an aspect ratio of two, the paper studies effect of the Moving Surface Boundary-layer Control (MSBC) on the fluid dynamics of a barge-like structure. The momentum injection was provided through two rotating cylinders forming vertical edges of the upstream square face. Wind tunnel results at a subcritical Reynolds number of 5x10(5) are complemented by the tow-tank experiments. Results suggest significant effect of the MSBC on both pressure distribution as well as forces acting on the barge. In general, the momentum injection leads to a delay in the boundary-layer separation and hence a reduction in the pressure drag. For the present case, wind tunnel results showed a reduction in the drag coefficient of around 24%, while the tow-tank study suggested a decrease of as large as 28% for a Fronde number of 0.18. It is important to point out that the MSBC is essentially a semi-passive process. The rotating elements are hollow cylinders and the power required in overcoming the bearing friction as well as fluid resistance is rather small. Results suggest that for an input of 1W, there is at least 8W reduction in power due to the decrease in drag. A brief video will accompany the presentation.