Computational simulation of rotating noise of fan

A rotating fan could produce noise of both broadband and discrete frequency. The discrete part typically consists of shaft frequency, blade passage frequency (BPF) and their higher harmonics. The shaft-order noise, which is mainly induced by unbalanced rotating, is often hard to be eliminated. In this paper, the rotating noise caused by geometric asymmetry is discussed and predicted. Analytic point force model is firstly used to predict the noise at points in different directions. Then a hybrid method based on computational fluid dynamic (CFD) simulation and FW-H equation is used to predict the noise of a simplified fan model. Compared with the case of symmetric rotating, a case of asymmetric rotating is studied, and the results show that geometric asymmetry could cause the increase of fan noise considerably at certain frequencies.