Finite element models for predicting the propagation and radiation of fan noise from turbofan engines

Finite Element methods are presented for predicting fan noise radiation from turbofan aero-engines. Fan noise is a major contributors to whole aircraft noise for current High-Bypass-Ratio (HBR) aero-engines. The work reported here seeks to develop robust prediction methods for forward and aft-radiated noise which can be used to study and optimize the acoustic design of engine ducts. The current article focusses on propagation through the by-pass duct. Two hybrid methods are described in which in-duct propagation is predicted by using two different Finite Element approaches. Both are designed to model the effects of non-axisymmetric liners within such ducts. In both cases, radiation is dealt with by matching an in-duct finite element solution at the exhaust plane to an analytic radiation model which takes into account refraction through the shear layer and reflection from a acoustically hard centrebody. Results will be presented to illustrate the capabilities of such models and a simple benchmark problem is presented in which the predictions obtained from each methods are compared for acoustic scattering by hard rectangular patch in a lined annular duct