Numerical Investigation of Blade Trimming Effect on Performance of Axial Flow Fan

Blade trimming is a simple and effective mean to solve the excessive margin of axial fans. For a variable-pitch axial fan of OB-84 type, the variation of performance curves with relative blade trimming quantity of 5%, 10% and 15%, respectively, are simulated when the tip clearance is changed and unchanged. The effects of blade trimming quantity and tip clearance on internal dynamics and operating performance are investigated, and the formulas of operating points before and after blade trimming are presented. The results show that both of full pressure and efficiency curves for the fan with blade trimming tend to decrease compared with the original one, and it is confirmed that the performance of the fan with tip clearance unchanged, near the design condition, is superior to that when tip clearance changed, which is contrary to the large flow rate. The margin of parameters provided by original design is so large that the fan usually operates at the left side of rated load; therefore, the blade trimming of axial fan should keep tip clearance unchanged in order to maintain better performance. The tip clearance has a significant effect on the formulas of operating points before and after blade trimming. The formulas given effective to predict the actual trimming amount of blades, which provide an important reference for blade trimming in practical applications of axial fans.