Sameer I. Madanshetty
Aerospace and Mech. Eng., Boston Univ., 110 Cummington St., Boston, MA 02215
Yale Univ., New Haven, CT 06520
A method of controlling noise level in duct flows is described. The method is based on the principle of energy extraction by active source(s), rather than by wave cancellation as in ``antisound.'' As such, the method of energy extraction is robust; it does not need the delicate signal processing, perfect phase, and amplitude matching, crucial to sound cancellation. An improved control strategy useful for both low and high frequencies is described, and its effectiveness in the presence of mean flow is analyzed. It is found that in the presence of through flow the control is effective in extracting energy from any waves traversing it. As the duct flow Mach number increases the control appears to be less effctive for waves produced upstream of it but it is more effective for the waves produced downstream of the device. Further, this conclusion remains valid whether the detector is placed on the upstream or downstream side of the control device.