Turbofan broadband noise predictions using a 3-D ZDES rotor blade approach

Abstract

Turbofan broadband noise prediction is a major concern for industry and probably the most challenging issue for Aeroacoustic community. The dominant source mechanism is attributed to the rotor turbulent wakes impacting on the outlet guide vanes. Unsteady computations of the full rotor-stator stage are generally out of reach so that interaction noise is commonly assessed using analytical models (related to Amiet's theory) and averaged turbulence characteristics issued from a steady RANS calculation and isotropic homogeneous turbulence assumption. However these models are questionable to accurately describe the turbulent rotor wakes characterized by a non-uniform spatial distribution stretched in the flow direction. Thus, a hybrid method based on a 3-D Zonal Detached Eddy Simulation of the flow around a single rotor blade is investigated to provide a full description of the turbulent wakes directly used in the Amiet-based code. The reliability of this approach is checked thanks to the comparisons of turbulent velocity and acoustic spectra respectively with hot-film probe and microphone measurements performed in Snecma engine test rig. A quite good agreement is shown between numerical and experimental turbulent velocity spectra and also the von Karman spectrum model, when mean turbulence characteristics are well adjusted. Moreover, sound pressure and power spectra in the outlet duct predicted by ZDES-Amiet coupling are reasonably close to the available measurements, and not so far from RANS-based ones.