Noise level of AC (Air-Conditioner) outdoor unit fan system has always been receiving much concern. It involves both aerodynamic noise and vibroacoustic noise. But most previous studies have been focused on aeroacoustics, and less attention is paid to the latter.
The objective of present study is to identify the influential factors of vibroacoustic noise and quantify its contribution to the overall noise level of the fan system. A numerical approach has been developed for predicting the flow-induced fan casing vibration and noise radiation. A fluid-solid-sound unidirectional coupling technique is used to transfer the unsteady loading to the structure, and the results arising from structural vibration analysis are used as sound radiation boundary conditions. Unsteady fan flow is solved by Large Eddy Simulation (LES) method. Then, the fluid force produced by the fluctuating pressure component acting on the inner casing surfaces is obtained, and it is used as external excitation in the Finite Element Analysis (FEA) model of the casing structure. Further, harmonic response analysis is conducted and the obtained results are used to calculate sound radiation through Indirect Boundary Element Method (IBEM), while the displacement amplitude obtained in structural analysis is used as boundary condition.
Experimental tests are conducted respectively on fan aerodynamic and aeroacoustic performance, and casing vibration. The numerical approach is partially validated by the experimental data. The validated models are used to predict the vibroacoustic noise, based on which, a quantitative evaluation of its contribution to overall sound level is conducted.