Integrating CFD source predictions with time-domain CAA for intake fan noise prediction

Abstract

A method is proposed for integrating a source prediction obtained from a Computational Fluid Dynamics (CFD) model for the fan stage of a turbofan engine with a Computational Aero-Acoustics (CAA) propagation code to predict tonal noise radiation in the far field. The Reynolds-Averaged Navier-Stokes equations are used to model the generation of the tones. Their propagation through the intake is simulated by applying the Discontinuous Galerkin Method to solve the linearized Euler equations in the time domain. The CFD and the CAA solutions are matched in a region where both solutions overlap and where non-linear effects, important close to the fan, can be considered to be less significant. An equivalent modal source on a notional source plane behind the fan is used to duplicate the sound field in this matching region and is then to drive a fully three-dimensional CAA radiation model for a near-field acoustic solution. The far-field sound pressure is obtained by applying the Ffowcs Williams-Hawkings formulation on a porous surface within the CAA domain. The accuracy and efficiency of this approach are investigated and results obtained are compared to measured data from a fan rig.