Supersonic fan tones are a critical issue for large fans; it is well known that thesetones are a key noise source at high power operating conditions for modern turbofan aero-engines. Nonlinear propagation of the rotor-locked pressure field generated in a turbofan intake duct is calculated by implementing nonlinear weak-shock theory numerically via a combined time-frequency domain algorithm. The aim of the prediction method is to model the nonlinear attenuation and liner absorption of the rotor-locked pressure field within the intake duct. In this hybrid method, the time-domain approach provides a robust and accurate prediction of the non-linear attenuation while the frequency domain is required to represent the liner attenuation. The focus of this work is to compare the time-frequency domain method with time-domain or frequency-domain methods which have been developed previously to calculate the nonlinear propagation of the rotor-locked pressure field in either a rigid or lined intake duct respectively.The capability of the time-frequency domain method to calculate accurately the nonlinear propagation of the rotor-locked pressure field, which can provide an engineering method for buzz-saw noise prediction, is demonstrated.
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