Control Of Forebody Flow Asymmetry In High-Angle Flows

Dynamic manipulation of forebody vortices as a means to obtain directional control of high-performance aircraft at high angles of attack is investigated. A tangent ogive shape of a slender body of the revolution is chosen as most representative of a real nose geometry of either a missile or military aircraft.In order to determine the characteristics of forebody flow asymmetry, a systematic study of the lee-ward flow field over a slender body of the revolution on the extreme high-angle-of-attack is conducted at a low-speed wind tunnel in Nanjing University of Aeronautics and Astronautics. The flow field on the lee-ward of the forebody at large incidence were scanned by a seven hole probe and PIV system. A predominant feature of vortical structure is yield.Investigations of the behaviors of the flow over the slender cylindrical body with the disturbances are conducted. A slim cylinder is placed in the upstream of the slender body to make a easy-control disturbances source with its wake flow. Effects of the free stream turbulence and the minute asymmetry of the nose tip on forebody asymmetric vortex are studied as well. In addition to the force measurement, dynamic surface pressure data were collected, as well as off-surface flow visualization. The experiments show that the bi-stable forebody vortex pattern under the control of disturbances group make a random vortex switching between its two stable states with very low frequency. The fixed mini-nose-tip-strake can lock the asymmetric vortex pattern and the direction of side force within the entire range of high angles of attack.Effectiveness of the swinging mini-nose-tip-strake technique for controlling forebody vortex asymmetry at high angles of attack is investigated. The new method was effective in suppressing side force to zero level with only very small energy input at high angles of attack (30°