Novel error sensing microphone arrays for active control of turbofan rotor/stator tones

Active control of turbofan rotor/stator interaction tones is complicated by the simultaneous presence of multiple duct propagation modes. In‐duct error sensing microphone arrays that can adequately resolve these modes typically require duct lengths that are incompatible with modern compact engine design. Two alternative approaches have been investigated. For inlet noise, an external linear array of microphones was positioned in the near/far radiation field transition region and weighted to provide error signals resolved either by duct mode or by radiation angle. For the exhaust, radially spaced microphones have been placed on duct bifurcation panels to provide supplemental radial‐mode resolution. The concepts were tested in combination with an adaptive segmented liner in a static duct and as part of an active stator‐vane system in the ANCF research facility at NASA/Glenn Research Center. [Work sponsored by NASA/Langley Research Center.]