Control of Rotorcraft Retreating Blade Stall Using Air-Jet Vortex Generators

A series of low-speed wind tunnel tests was carried out on an oscillating airfoil fitted with two rows of air-jet vortex generators (AJVGs). The airfoil used had an Royal Aircraft Establishment 9645 section, and the two spanwise arrays of AJVGs were located at x/c = 0.12 and 0.62. The devices and their distributions were chosen to assess their ability to modify/control dynamic stall, the goal being to enhance the aerodynamic performance of helicopter rotors on the retreating blade side of the disk. The model was pitched about the quarter chord with a reduced frequency k of 0.1 in a sinusoidal motion defined by a = 15 + 10sin ωt deg. The measured data indicate that, for continuous blowing from the front row of AJVGs with a momentum blowing coefficient C μ greater than 0.008, modifications to the stalling process are encouraging. In particular, the pitching moment behavior exhibits delayed stall and there is a marked reduction in the normal force hysteresis.