Ran Cabell
Virginia Polytech. Inst. and State Univ.---Virginia Consortium of Eng. and Sci. Universities, 2713-D Magruder Blvd., Hampton, VA 23666
Chris Fuller
Virginia Polytech. Inst. and State Univ., Blacksburg, VA 24061
An analytical study of the active control of fan noise in a turbofan engine with wall-mounted acoustic sources is described. The transfer functions between the acoustic sources and microphones outside the duct are decomposed into principal components (PCs). The active control problem is then solved using a subset of the principal components. The subset consists of PCs that are statistically significant for accurately modeling the primary radiated noise. The resulting elimination of certain PCs is a mathematically efficient way to optimally reduce the number of channels of control. In certain cases it can be shown that the PCs describe the radiating modes of the control system. This provides substantial insight into the mechanisms of control, and can be used in the controller to derive specific modes to the exclusion of all other modes. [Work supported by NASA Langley Research Center.]