Active Control of Turbomachine Discrete Frequency Noise Utilizing Oscillating Flaps and Pistons

Abstract

Turbomachine discrete frequency tones are a signi® cant environmental concern. These tones are generated by periodic blade row interactions, with only speci® c circumferential acoustic modes generated. This research is directed at active control of discrete frequency noise generated by subsonic blade rows through cancellation of the propagating acoustic waves, accomplished by utilizing airfoil surface mounted oscillating actuators to generate additional control propagating pressure waves. These control waves interact with the propagating acoustic waves, thereby canceling the acoustic waves and thus the far-® eld discrete frequency tones. A series of experiments are described, directed at investigating the fundamentals of this active discrete frequency noise control technique as well as verifying basic modeling assumptions. Both an isolated vane and a three-vane row are utilized, with the