Tone noise prediction of an open-fan engine using a source-mode integral formulation

This study discusses the development of a tone noise model dedicated to an open fan engine, also called Unducted Single Fan.Because of its particular architecture, this engine aims to reduce fuel consumption, but it might increase the radiated noise due to the fairing removal.This model intents to be soon implemented into acoustic source mapping techniques to better characterize the dominant sources in future wind tunnel experiments.It is based on FW-H analogy relying on the thickness and loading noise terms of Goldstein's formulation, written in the frequency domain.A decomposition into angular modes through equivalent fixed phase-shifted sources is proposed.The predicted sound field takes in account different contributions, which are investigated here: the thickness noise, the steady and unsteady loading noise (from rotor and stator) in forward flight configurations, and including nearfield effects.The unsteady loading harmonics are obtained from URANS calculations with eslA ONERA code.First predictions are compared to reference solutions provided by a time-domain FW-H solver, with fully non-compact sources involving a complete surface integration, at approach operating point.A more practical compact-source form is presented too.