Research on the broadband noise characteristics of fan annular cascade based on flow-field/acoustic-field hybrid model

Fan noise is an important noise source of high bypass ratio turbofan engines, mainly composed of tonal noise and broadband noise. As the level of fan tones is reduced, the research on broadband noise has been paid more and more attention. This article takes the fan annular cascade as the research object. Firstly, numerical simulations are carried out by using the Delayed Detached Eddy Simulation (DDES) and the flow-field/acoustic-field hybrid model (DDES/LAA), and the purpose is to study the influence rules of the rotor rotation speed and the inlet velocity of the fan annular cascade on its broadband noise. Secondly, in the semi-anechoic chamber of the Aero-Acoustic Laboratory of Northwestern Polytechnical University, the acoustic field of the fan annular cascade is experimentally studied and verified by using a multi-row circular microphone array. The results show that the broadband noise sound power level of the fan annular cascade increases significantly with the increase of the inlet velocity. There is an obvious "hump" in the noise spectrum curve, and this "hump" migrates to higher frequencies as the rotor speed and the inlet velocity increase. Both the numerical simulation and experimental results indicate that the central frequency of the "hump" structure basically corresponds to the shedding vortex frequency of the rotating rods in the fan annular cascade, suggesting that "hump" noise is caused by the interference between the shedding vortex generated by the rotating rods and the downstream cascades. By understanding the relevant characteristics of the broadband noise of the fan annular cascade, this study provides a reference for the noise reduction methods of the broadband noise of aero - engine fans.