ACTIVE ACOUSTIC SUPPRESSION OF CASCADE FLUTTER BY MEANS OF ACTUATOR SURFACE ON THE DUCT WALL

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Experimental verification of active acoustic flutter control was successfully conducted on the basis of a single airfoil under coupled flexure-torsion flutter at low speeds and low frequencies in a wind tunnel with loudspeakers mounted on the wall.New test facilities for higher speeds (about 120 m/s) and higher frequencies (about 150 Hz) have been constructed.Calculation codes to predict unsteady aeroynamic force on vibrating cascade blades interacting with acoustic waves from a vibrating actuator surface on the duct wall were developed for subsonic and supersonic linear cascade models and a subsonic annular cascade model. Comprehensive parametric studies have been conducted, and the optimun geometry and motion of the actuator surface for various cases were made clear.The research is being extended to acoustic suppression of unsteady blade loading and noise due to interaction of cascades with oncoming gusts. Some new findings have been obtained.