Computational AeroAcoustics of Realistic Co‐Axial Engines

Abstract

This study, that is relevant from the turbofan engines noise prediction/reduction, aims at CAA‐computing the aft fan noise propagation/radiation of a realistic full‐3D exhaust (with pylon and internal bifurcations), the latter being affected of (i) typical in‐flight (take‐off) thermodynamic conditions and of (ii) a representative fan noise modal content. As for previous studies conducted over baseline geometries, this CAA computation is conducted following the usual hybrid process, where a preliminary aerodynamic calculation provides a heterogeneous steady mean flow on which an acoustic calculation is then conducted A RANS computation is first performed, delivering the stationary jet mean flow characterizing the 3D exhaust in its typical 'take‐off flight' (M∞ = 0.25). A CAA grid (22 blocks, 28 millions cells) is then derived from the CFD one, before the RANS steady jet mean‐flow is interpolated on it. After what the CAA computation is computed, a fan noise mode (26, 1) being emitted at a reduced frequency of kR = 30 (1 BPF) in the upstream of the engine's secondary exhaust, and numerically propagated along and outside the latter. Finally, a Kirchhoff post‐treatment provides the far‐field radiation characterizing these engine geometry, modal content and thermodynamic conditions.