An Improved Passage-flow Turning Model for Forward-curved Blades of Squirrel-cage Fan

Abstract In the present study, an improved passage-flow turning model (IPTM) was proposed to design high-performance forward-curved blades for squirrel-cage fans. The flow separation in blade passages and the corresponding fan performance were compared between IPTM and traditional methods through computational fluid dynamics (CFD). The results show that the blade inlet angle requires correction based on the zero-incidence design, or the passage mainstream will separate from the blade pressure surface, which is detrimental to the fan performance. It is also found that the blade shape with 2nd-order smoothness owns the thinnest separation and highest efficiency when other design parameters are the same. After taking these two points into consideration, the blades designed by IPTM performs significantly better than the traditional blades with the same inlet and outlet angle. According to CFD results, the optimal value of the turning radius R¯T and the decelerating factor of the leading-half blade e was suggested. The designed blade achieves high pressure when these two parameters satisfy R¯T=−0.185ε+0.29175, while achieves high efficiency when they satisfy R¯T=−0.31ε+0.4425. In order to validate the advantages of IPTM, the optimal blade designed by IPTM was manufactured and measured. Results show that the maximum increase in fan pressure and efficiency were over 10% and 6 percentages, respectively.