Cyclostationarity of the noise radiated by a rotating acoustic source in a duct: Proof of concept

The fan of an aero-engine, as a classical rotating structure, is located in the culvert (duct) and is a significant source of noise. Cyclostationary theory is widely applied in signal processing for rotating machinery. Therefore, the main objective of this paper is to demonstrate that the noise radiated by a rotating source in a duct is cyclostationary. Firstly, the Wold–Cramer decomposition form of the propagation equation for a rotating point source in a duct is derived. This decomposition is then used to demonstrate the cyclostationarity of the sound field radiated by a rotating point source in a duct is explained. Next, the theory is extended to a rotating blade source. Then, the cyclic spectral characteristics of several rotating sound sources in a duct are derived. It is worth mentioning that the broadband noise radiated by a fan inside a duct is still cyclostationary. Finally, the correctness of the proposed theory is verified by using rotating monopoles inside a duct, and the SJTU 1.5-stage compressor.