Advanced modeling of active control of fan noise for turbofan engines

An advanced model of active control of fan noise for turbofan engines is being developed using the ducted fan noise prediction code TBIEM3D [M. H. Dunn, NASA/CR‐97‐206232, Sept. 1997]. An engine fan surrounded by a duct of finite length and cylindrical profile, translating in its axial direction with a uniform speed, is considered. A collection of spinning line sources located inside the duct are used to simulate the fan noise. Control sources modeled by point monopoles are placed along the duct inner wall to generate the secondary field that destructively interferes with the fan noise. A feedforward active noise control algorithm is simulated. Test cases were performed to demonstrate the feasibility of the model to perform active noise control studies. First‐ and fourth‐order circumferential modes generated at a blade passage frequency of 1000 Hz were generated and targeted for control using far‐field and inlet error sensors combined with a rigid or lined duct inner wall. Interference between inlet and outlet radiation, as well as the reflection from the duct openings and near‐field effects were included. This model was found to be accurate, fast, and versatile. [Work supported by NASA Langley Research Center.]