Integral techniques for jet aeroacoustics calculations

Abstract

Reducing aircraft noise by a factor of four in the next twenty years is one of NASA's goals. Major reduction in acoustics emissions of aircraft jet engines is only possible with a reduction in jet noise. Hence, there is a need for improving the current state-of-the-art jet noise prediction methodology. We have developed in the past a Kirchhoff method code in order to evaluate the acoustic signals from an unsteady CFD code. In this paper, an integral acoustic code based on the porous Ffowcs Williams-Hawkings (FW-H) method is developed for the noise prediction of three-dimensional turbulent jets. The porous FW-H method can be more robust than the Kirchhoff method with regard to the choice of control surface, hence our efforts are focused in the development of the porous FW-H method. The resulting FWH code also includes refraction corrections to account for the zone of silence, as well as techniques to include acoustic sources outside the CFD domain. The code is validated for point sources. Once validation is complete, the code will be used to study the aeroacoustics of a three-dimensional turbulent jet at a Reynolds of number of 500 and possibly of another turbulent jet at a Reynolds number of 3600. The control surface needed for the FW-H method will be outside the jet flow, but inside the CFD boundaries in order to avoid boundary effects. The quantities on the control surface will be obtained using a Direct Numerical Simulation (DNS) code. The radiating sound will then be evaluated using the acoustics code developed herein.