Effects of blade stagger angle adjustment on the flow and noise of a counter-rotating fan

Abstract

To improve the performance of a counter-rotating fan (CRF) installed in an outdoor unit of centralized air conditioner with the complicated inflow condition, a parameter study on the blade stagger angle (BSA) of the forward and rear rotors is performed. 9 BSA schemes are designed with an angle variation from −4° to 12°. Both experimental test and Delayed Detached Eddy Simulation (DDES) are conducted to analyze the influence of BSA adjustment on the flow structures and noise features of the CRF. As a result, the blade leading edge pressure fluctuation is weakened effectively by means of increasing the forward and rear rotors BSA properly, and lower fan noise can be achieved. While once the BSA exceeds the optimal value, the fan noise would be increased due to the enhanced pressure fluctuation induced by the suction side flow separation and tip leakage flow in the rear rotor. In this study, as the BSA of the forward and rear rotor are increased by 6° simultaneously, the fan noise reduction is most prominent, and the overall sound pressure level is lowered by 1.56 dB(A).