ACAT1 Fan Stage Broadband Noise Prediction Using Large-Eddy Simulation and Analytical Models

The present paper deals with the assessment of the turbulent flow through and the noise radiation of the ACAT1 fan stage, which was tested in the framework of the European project TurbonoiseBB. It aims at analyzing and predicting the broadband noise resulting from the impact of the fan wakes onto the outlet guide vane (OGV) at approach condition. This is achieved via a large-eddy simulation (LES) of the full fan-OGV stage that is in good agreement with the mean flow measurements. Some disparities regarding the turbulent content of the flow are, however, highlighted. The main flow features and the broadband noise sources are examined. The noise is then estimated using two different hybrid approaches: LES-informed analytical models, using Hanson's and Posson's cascade models, and a numerical approach coupling the LES with the free-field Ffowcs Williams and Hawkings (FW-H) analogy, and Goldstein's in-duct acoustic analogy. The shape of the noise spectra provided by the analytical models is relatively similar to that of the sound measurements, whereas some discrepancies on the absolute noise levels may appear depending on the analytical model and the turbulence length scale estimate. The numerical approach reveals that accounting for the duct effect through Goldstein's analogy provides noise levels much closer to the measurements than those obtained with the free-field analogy, which significantly overestimates the broadband noise. Both the analytical and the numerical approaches suggest that additional significant noise sources might be present in both the experiment and the simulation.