Zonal Detached Eddy Simulation of the Fan-Outlet Guide Vanes Stage of a Turbofan Engine: Part II—Broadband Noise Predictions

Abstract

This paper (Part II) presents the broadband noise predictions of a turbofan stage based on a hybrid method proposed by ONERA in the framework of the European project TurboNoiseBB. The numerical approach relies on a ZDES (Zonal Detached Eddy Simulation) strategy that is applied to a fan module at approach conditions and tested in AneCom facility (Wildau, Germany). The ZDES method with main aerodynamic flow features is detailed in a companion paper (Part I), and this one focuses on acoustic analyses. Acoustic codes based on Amiet's theory and FWH (Ffowcs Williams and Hawkings) analogy, both taking into account for duct propagation effects, are briefly described in the article and chained to the computational fluid dynamics to assess the rotor–stator interaction (RSI) noise (focusing on stator sources). The required inputs are the turbulent wake information (issued from either Reynolds Averaged Navier-Stokes (RANS) or ZDES) in front of the stator and the unsteady pressure on the vane wall, respectively. Turbulent velocity profiles and velocity spectra are compared to hot-wire measurements in the interstage region. A nice agreement is globally observed with a clear improvement compared to RANS solutions. Then, sound power spectra in the intake and bypass duct provided by acoustic codes are discussed and compared to the experiment. Reliable numerical predictions are obtained when undesirable additional sources in the rear-chord region (believed to be caused by local flow detachments from the vane leading edge and near the trailing edge) are removed from the FWH surface integration. ZDES + FWH spectra are found to be not so far from RANS + Amiet ones, with a best fitting to the experimental spectrum shape and predicted levels 3 dB below the measurements.