Numerical prediction of the interaction noise radiated from an axial fan

The rotor–stator interaction noise in axial fans is mainly caused by the periodic wake from the rotating fan impinging on the stator rows downstream. In order to accurately predict the noise, a thin-body BEM/Curle method is developed in this paper. It is a hybrid method combining computational aeroacoustic with Boundary Element Method (BEM) and can be used to predict the propagation of sound wave in the duct. The calculation includes three steps: firstly, the unsteady viscous flow around the blades is calculated using the CFD method to acquire the noise source information; secondly, the radiated sound pressure is calculated using the acoustic analogy Curle equation in the frequency domain; lastly, the scattering effect of the duct wall on the propagation of the sound wave is expressed using the thin-body BEM method. In comparison with the experimental results, the predicted sound pressure levels (SPLs) are correct in the Blade Passing Frequency (BPF) and its harmonics. The sound pressure directivities of sound source and scattering effect are shown in the paper. The conclusion is that the scattering effect of the duct wall cannot be ignored in the prediction of rotor–stator interaction noise and can increase the accuracy of the prediction in comparison with the results based on the free-field assumption.