Reduction of Separation Noise by Using an Imaginary Control-Device

Hypothetical method for reducing separation noise of a two-dimensional airfoil with a high angle of attack was investigated numerically. The method was based on suppression of local surface-pressure fluctuations in a small area in a cordwise direction. The area in which the pressure fluctuations were suppressed was regarded as a working area of an imaginary actuator. The effect of the actuator on reduction of the separation noise was investigated. The sound pressure level of the separation noise was found to be sensitive to the setting position of the actuator. The separation point near the leading edge on the suction side and the separation point near the trailing edge on the pressure side were found to be the effective positions of the actuator for reducing the separation noise.