Numerical Study on the Influence of Blade Tip Slot and Winglet on the Performance and Noise of Axial Fans

For a two-stage variable-pitch axial fan, a new type of blade tip structure with suction surface winglets and carve slots was proposed. The aerodynamic performance of the fan before and after modification was simulated by Fluent software, and the noise and vortex changes were obtained by large eddy simulation. The influence of blade tip structure on the performance, internal flow, noise and vortex structure at the blade tip was analyzed. Results show that the total pressure and efficiency of the fan are improved after the installation of the winglet on the suction surface, the best performance is achieved after setting a downstream-slot on the winglet. The leakage vortex and blade tip clearance are the main noise source, and the winglet on the suction surface can effectively reduce the acoustic noise, while the slotted winglet results in the increase of total sound pressure level. Considering both the performance and noise changes, the scheme 2 is the best modification scheme. Under this scheme, the reduced leakage vorticity at the blade tip, the low fan noise and the scattered distribution of vortex structure are observed. The large-scale vortex breaks into small pieces, and the vortex core is far away from the main channel, resulting in smaller blade tip losses.