Parametric investigation of the effects of active flow control on the normal force of a delta wing

The efficacy of active flow control in delaying vortex breakdown and enhancing the lift characteristics of a 70°-sweep delta wing is experimentally investigated in a low-speed wind tunnel at the USAF Academy. Periodic blowing and suction with zero net mass flux is applied at the leading edge of the wing. The pressure distribution over the upper surface of the wing is measured at a freestream velocity of 4.3 m/s, corresponding to a chord Reynolds number of 2.1×10⁵. A parametric study is conducted, aimed at investigating the effect of periodic flow excitation on the pressure distribution on the upper surface of the wing. In particular, the normal force is computed and optimum values of key control parameters are established. The momentum coefficient of the flow excitation is varied from 0 to 0.004 and the nondimensional frequency is varied from 0 to 3.5. Pressure distribution on the upper surface of the wing is measured at angles of attack of 20° to 40° and the pressure is integrated to yield the normal force coefficient. It is found that the periodic flow excitation delays wing stall and greatly increases the normal force at angles of attack where stall would have occurred otherwise. At a constant momentum coefficient, the effect of the flow excitation is maximized at a nondimensional frequency of 1.38. At a constant frequency, an almost asymptotic increase of the normal force is observed as the momentum coefficient increases. The effect of the periodic flow excitation reaches its maximum at a momentum coefficient of 0.004 approximately. These results are consistent with results that were obtained in previous investigations. A maximum increase of 38% in the normal force is obtained at an angle of attack of 40o at the test conditions, relative to the unforced case. A 10o delay of the stall angle is achieved.