Fan tone noise generation in modern turbofan engines can be impacted significantly under real installation conditions where the fan operates in non-uniform inflow and is subject to back pressure distortion. This paper presents a numerical study of the tonal noise produced in a turbofan engine with focus on the identification of fan-related noise mechanisms under realistic installation conditions and their impact on inlet and aft noise radiation. The fully coupled CFD simulation considered here includes the inlet, fan, and exit guide vanes in the bypass and core ducts, as well as additional struts and the pylon bifurcation. It is found that for the present case inlet tonal noise is dominated by inflow distortion effects due to the drooped inlet, while rotor-stator interaction noise and fan back pressure distortion have a small impact. The inflow distortion interacts with fan shock waves and modifies their propagation through the inlet. For aft-radiated noise different mechanisms were identified. Due to the presence of the pylon bifurcation, the blade-passing frequency (BPF) tone that is nominally cut-off is being scattered into neighboring propagating modes. At higher harmonics of the BPF, the aft noise is dominated by rotor-stator interaction modes. Inlet noise power level predictions including the acoustic liner were performed with a hybrid CFD/CAA approach, while aft noise predictions were made directly from the CFD results using a modal filtering technique. Power level predictions were overall found to be in good agreement with full-scale engine ground test data. This paper highlights the importance of including installation effects in noise predictions and presents a comprehensive approach for turbofan inlet and aft tonal noise predictions.
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