Abstract:

This paper summarizes the recent advances in the active control of tonal inlet noise from an operational Pratt and Whitney JT15D turbofan engine. The most recent results show that multiple circumferential control source arrays reduce the radiation spillover to the sideline that is often observed with a single control array. An optimal control configuration results in near global attenuation in all directions of the directivity field, and a sound power reduction of 5.1 dB. A power reduction of 4.1 dB was obtained over a desired sector spanning the angles from 40 to 60 degrees in the far field using a properly configured control system. Results using a hybrid passive-active inlet have also been obtained showing that a passive liner in combination with an active control system will eliminate much of the sideline control spillover. An inlet-mounted sensing strategy using a wave-number observation technique was implemented and the preliminary results show the potential of the method for eliminating far-field microphones. The latest results utilizing hybrid passive-active control with far-field and inlet mounted sensors will be presented and discussed. [Work supported by NASA Langley Research Center.]