Variation of Sound Directivity From a Supersonic Nacelle

Abstract

The effects of aircraft flight speed and fan face pressure variations on sound propagation from an axisymmetric commercial supersonic engine inlet were studied using numerical methods. A computational fluid dynamics (CFD) model of the inlet was constructed in Ansys Fluent. The results of this model were then used as inputs for the aeroacoustic solver, ACTRAN, and used to calculate far field radiated noise. Using this process, a parametric study was conducted varying two parameters: the approach Mach number from 0.35 to 0.55 in increments of 0.0125, and the fan face back pressures from −10 kPa to −40 kPa in increments of 1 kPa. It was found that variations in free stream Mach number resulted in approximate variations of 2 dB on radiated acoustics while variations in fan face pressure resulted in up to 5 dB of change. These variations were found to be frequency dependent with the largest variations happening over a frequency range of approximately 3 kHz to 5 kHz and again from 6 kHz to 8 kHz. These results indicate combinations of flight speed and fan pressure to avoid in flight to reduce overall noise reaching the ground.