Abstract

This part II paper presents the broadband noise predictions of a turbofan stage based on an 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 condition and tested in AneCom facility (Wildau, Germany). The ZDES method with main aerodynamic flow features are 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, briefly described in the article, are chained to the CFD to assess the rotor-stator interaction noise. The required inputs are the turbulent wake information (issued either from RANS or ZDES) in front 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 noticeable improvement compared to RANS solutions. Then, sound power spectra in the intake and bypass duct provided by acoustic post-processing are discussed and compared to the experiment. Reliable numerical predictions are obtained when undesirable additional sources (shown to be caused by local flow separation at the vane wall) are removed from the FWH surface integration. ZDES-FWH spectra are found to be not far from RANS-Amiet ones, with a best fitting to the experimental spectrum shape and level deviations within 3 dB.

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