MOVING SURFACE BOUNDARY-LAYER CONTROL: A REVIEW

The paper briefly reviews developments in the exciting field of the moving surface boundary-layer control (MSBC). To begin with, application of the concept to a family of two-dimensional airfoils, investigated experimentally, is briefly summarized. The moving surface was provided by rotating cylinders located at the leading edge and/or trailing edge as well as the top surface of the airfoil. Results suggest that the concept is quite promising, leading to a substantial increase in lift and a delay in stall. Depending on the performance desired, appropriate combinations of cylinder location and speed can be selected to obtain favourable results over a wide range of the angle of attack. Next, the effectiveness of the concept in reducing drag of bluff bodies such as a two-dimensional flat plate at large angles of attack, rectangular prisms, and three-dimensional models of trucks is assessed. Results show that injection of momentum through moving surfaces, achieved here by introduction of bearing-mounted, motor-driven, hollow cylinders, can significantly delay separation of the boundary layer and reduce the pressure drag. The momentum injection procedure also proves effective in arresting wind-induced vortex resonance and galloping type of instabilities, suggesting possible application in the next generation of civil engineering structures. Now the attention is directed towards the role of computational fluid mechanics to this class of problems. The system performance, as predicted by results obtained using two distinctly different numerical procedures, shows good correlation with the wind tunnel data. Finally, results of a flow visualization study, conducted in a closed-circuit water tunnel using slit lighting and polyvinyl chloride tracer particles, are touched upon. They show, rather dramatically, the effectiveness of the MSBC.