Research on the Aerodynamic Noise Performance of a Novel Structure of Cooling Fans in Series

Abstract In systems with high downstream flow resistance, a single fan is prone to operating in an unstable range and generating backflow downstream of the hub. Conventional fans in series could overcome system resistance by increasing the pressure rise capacity. However, conventional fans in series do not improve the flow deterioration in the hub area of a single fan but instead posed a serious challenge to the system’s noise reduction effect due to its complex structure. A novel structure of cooling fans in series using two different-sized fans is designed and manufactured, and the aerodynamic and acoustic performance of a series structure with a smaller-sized fan installed downstream of a larger-sized fan is investigated. The downstream small fan aims to reduce the flow deterioration such as backflow in the hub area of the upstream large fan, thereby achieving performance improvement. Experiments have confirmed that there is an optimal matching range between the speed of the large fan and the speed of the small fan under free-field conditions. The measured results of outlet wind speed indicate that the downstream flow field of the novel structure of fans in series is more uniform within this matching speed range. Noise and aerodynamic performance tests have shown that in the presence of system resistance and backflow conditions, the novel structure of fans in series can achieve higher aerodynamic performance at a total sound pressure level close to the prototype structure, achieving a maximum flow rate increase of 1.4% with only a 0.02 dB increase in noise. However, there is no severe backflow in the hub area under the free flow condition, and the new structure cannot fully play its role, resulting in a decrease in aerodynamic performance. The proposal of the novel structure of cooling fans in series can provide more options for the design of heat dissipation modules in different impedance systems.