Surface Integral Methods in Jet Aeroacoustics: Refraction Corrections

Abstract

One of the major challenges in computational jet aeroacousties is the accurate modeling and prediction of acoustic fields to reduce and control the jet noise. Surface integral methods (e.g., the Kirchhoff method and Ffowcs Williams-Hawkings method) can be used in computational aeroacoustics to extend the near-field computational fluid dynamics results to far field. The surface integral methods can efficiently and accurately predict aerodynamically generated noise provided the control surface surrounds the entire source region. However, for jet noise prediction, shear mean flow exists outside the control surface that causes refraction. Mean flow refraction corrections for the surface integral methods have been done in the past using simple geometric acoustics. A more rigorous method based on Lilley's equation is investigated here due to its more realistic assumption of the acoustic propagation. Jet noise computational results based on large-eddy simulation for the near field of an isothermal jet at Reynolds number 400,000 are used for the evaluation of the solution on the Ffowcs Williams-Hawkings control surface. The proposed methodology for prediction of far-field sound pressure level shows that the acoustic field within the zone of silence is consistent with the measured data.