Active Control of Fan Noise Using Distributed Phased Pulsed Flows

A program for the development of an active pulsed flow noise control solution for turbomachinery noise caused by rotor wake interactions with stators is proposed. The system utilizes an array of pulsed jet flows near the leading edges of several stator blades to generate volume velocity sources to counter the fluctuating lift dipole sources caused by the wake-stator interaction. By placing the acoustic canceling sources adjacent to the location of the dipole sources rather than on the inner surface of the nacelles, better more efficient control of particularly the higher order radial modes can be achieved. Other advantages of the proposed noise canceling method are its extremely small size and light weight for producing a given sound power level. Lastly, the proposed system uses very small amounts of air available from the compressor and requires practically no electrical power, thus the heat generated and the weight required by conventional sound sources are largely eliminated. Initial laboratory tests indicate that this concept has the potential to meet and exceed the 115 to 120 dB re 1 pW sound power level that appears to be required from the work of previous investigators.