Aerodynamic Noise Characteristics of Axial Flow Fan in Narrow Space and Noise Reduction Based on Flow Control

The aeroacoustic characteristics of a power module in the electric vehicle charging pile is studied by experimental and numerical methods. In the free field, a single cooling fan mainly emits tonal noise, while the far-field noise of fans in parallel satisfied the superposition of incoherent sound sources. However, when two fans in parallel delivered air into the power module, the noise increased significantly, especially broadband noise. Referring to the power module, a narrow space model with cooling fan supplying air inward is constructed. The computational fluid dynamics (CFD) results show that the mass flow rate of the fan is reduced due to the obstacles downstream, which weakens the heat dissipation performance. Part of the fluid forms reflux, interacts with the fan and strengthens the corner vortex. By setting guide holes on the casing near the flow blockage to arrange flow, the flow resistance is reduced and the total mass flow rate of the fan is increased by 2.5%. The reflux and corner vortex are dispersed, and the vortices develop downstream, thus reducing the interaction with the fan. The predicted tonal sound pressure level (SPL) decreases by 3.2 dBA based on acoustic analogy method. The broadband noise caused by shedding vortex is also predicted and discussed by a semi-empirical model. In the noise reduction experiment of the real power module, combining inlet bellmouth on the fan and guide holes on the casing, the total SPL was significantly reduced by 2.9 dBA. Especially, based on bellmouth, guide holes brought an additional 1.9 dBA tonal noise reduction and 1.0 dBA total SPL reduction. The study indicates that appropriate flow control is important to improve the heat dissipation and reduce noise of the power module. These results are helpful to develop higher power charging system.