Influence of a Back-Flow Flap on the Dynamic Stall Flow Topology

Abstract

The dynamic stall phenomenon exerts a strong influence on the performance of highly loaded helicopter rotors in forward flight. Therefore, measures of flow control have been proposed to counter the negative impact of dynamic stall. The current wind tunnel experiments investigate a spoiler-type back-flow flap mounted on the suction side of the airfoil, which can be operated in either active or passive mode. A reduction of the Stall-related pitching moment of more than 25% was demonstrated. The focus of this work is a detailed evaluation of the flow field over the suction side of the airfoil, which will be investigated using high-speed Particle Image Velocimetry (PIV). The analysis allows a correlation between aerodynamic forces on the model and corresponding flow phenomena such as separation or dynamic stall development.