Comparison of Three Strategies for Buzz-Saw Noise Propagation in an Aeroengine Intake with Flow Distortion using CFD

The expense of computational methods that can accurately predict the tonal acoustic field in an aeroengine intake is a current limitation for understanding current and future challenges in aeroengine noise, such as the impact of increased flow distortion with UHBR (Ultra-High Bypass Ratio) turbofan designs. In this study, the intake propagation of shock-associated fan tone noise through a distorted inflow is considered. Three numerical methodologies are applied to explore novel methods for reducing the computational demand of representative and accurate calculations. The datum case considers the full intake domain with a fully structured computational mesh. A part-span approximation neglects low-span regions of the duct according to the observation that most of the interested acoustic content has energy focused towards the outer walls of the duct. Finally, a hybrid technique combines the earlier approaches by filling the previously neglected space with unstructured mesh. Both the part-span and hybrid methodologies unlock considerable computational savings. Both cases could sufficiently resolve the distorted flow field. The acoustic field at the first two Blade Passing Frequencies (BPFs) was considered for all cases. At the first BPF, both methodologies successfully represent the highest amplitude components. At the second BPF, more deviations were observed for the case that applied the part-span approximation, while the hybrid case results matched well with the datum case.