Investigations on a dynamic forebody flow control system

A novel method is proposed for the dynamic manipulation of forebody vortices of high-performance aircraft during flight at high incidence to provide increased lateral controllability when the control authority available from conventional control surfaces is dramatically degraded due to severe flow separation. The method takes advantage of the inherently bistable nature of the forebody vortices by deliberately switching them between their two stable states at a high frequency. Duty cycle modulation of the alternating blowing from two forward facing nozzles is used to control the mean lateral aerodynamic forces and moments. A series of wind- and water-tunnel experiments on ogive-cylinders and a schematic aircraft configuration have shown that by appropriately placing the nozzles, it is possible to obtain a linear relationship between duty cycle and mean control load, a highly desirable characteristic from a flight control point of view.