Drag Control Through Moving Surface Boundary-Layer Control on a Circular Cylinder

Drag forces on bluff bodies are directly proportional to the wake region downstream of the body, which is governed by the boundary layer separation point. These drag forces can be significantly reduced by delaying vortex separation and thereby decreasing a body’s wake region. This project examines the effectiveness of a method of boundary layer manipulation in delaying vortex separation of a cylinder in a cross flow. In this experiment, two smaller cylinders placed at 120^o directly downstream of the test cylinder were co-rotated to delay separation. This co-rotation acts as a moving wall thereby injecting momentum into the shear layers, a method known as Moving Surface Boundary-layer Control (MSBC) which minimizes the relative motion between the surface and the free stream, thereby retarding the growth of the boundary-layer.

Numerical models of zero net mass injection for flow manipulation surrounding a test cylinder have been conducted in the past for low Reynolds numbers based on diameter, Re=100-300. This experiment seeks to examine the effect experimentally at moderate Reynolds numbers based on diameter, Re=25000-100000, for which numerical models are difficult to construct. The efficiency of this method of MSBC was evaluated using the resulting drag coefficient of the test cylinder as well as by characterizing the resulting flow using laser doppler velocimetry (LDV).