Tonal Noise Prediction of a Modern Turbofan Engine With Large Upstream and Downstream Distortion

Abstract

Ultra-high bypass ratio (UHBR) engines are designed as compact as possible and are characterized by a short asymmetric air inlet and heterogeneous outlet guide vanes (OGVs). The flow close to the fan is therefore circumferentially nonuniform (or distorted) and the resulting noise might be impacted. This is studied here at take-off conditions by means of a simulation of the unsteady Reynolds-averaged Navier–Stokes (URANS) equations of a full-annulus fan stage. The model includes an asymmetric air inlet, a fan, heterogeneous OGVs, and homogeneous inlet guide vanes (IGVs). Direct acoustic predictions are given for both inlet and aft noises. A novel hydrodynamic/acoustic splitting method based on a modal decomposition is developed and is applied for the aft noise analysis. The noise mechanisms that are generally considered (i.e., interaction of fan-blade wakes with OGVs and fan self-noise) are shown to be impacted by the distortion. In addition, new sources caused by the interaction between the stationary distortion and the fan blades appear and contribute to the inlet noise.