Experimental study on side force alleviation of conical forebody with a fluttering flag

Slender bodies of revolution placed at high angles of attack will produce a steady asymmetric vortex pair. This behavior is determined by the spatial instability of the flow. The asymmetric vortex pair is very sensitive to small disturbances near the tip. This paper presents a simple side force alleviation method without a power unit for slender bodies at high angles of attack. The method uses the self-excited oscillation (flutter) of a small cantilever flag as the excitation source on the cone tip. An experimental study is performed to investigate the characteristics of the asymmetric side forces of a 20° cone-cylinder slender body with and without a small flutter flag. Pressure distribution at eight cross sections of the cone forebody is measured at different free-stream velocities and different angles of attack. The process demonstrates that the excitation provided by the fluttering flag can change the asymmetric bistable flow state to a well symmetric one at high angles of attack, and that the corresponding side force and yaw moment will significantly decrease. The flutter strength of the flag will be enhanced by increasing the free-stream velocity. The effectiveness of the side force alleviation method will also be increased.