Experimental study of the effect of blade tip clearance and blade angle error on the performance of mixed-flow pump

The hydraulic performance test of the mixed-flow pump has been carried out through selecting different blade tip clearances and various blade angle errors. The ratio of the mixed-flow pump efficiency reduction and the blade tip clearance variation (Delta eta/Delta delta) varies with the flow rate coefficient phi revealing a parabolic trend. An empirical equation has been developed for the mixed-flow pump model by parabolic fitting. For the same blade tip clearance variation Delta delta, the mixed-flow pump efficiency reduction Delta eta increases rapidly as the flow rate rises. For any given flow rate, the efficiency, the head and the shaft power of the mixed-flow pump all decrease with the increase of the blade tip clearance. Among them, the efficiency reduction Delta eta varies approximately linearly with the blade tip clearance variation Delta delta. When the angle of an individual blade of the mixed-flow pump has a deviation, the performance curves will move and change. These curves have consistent change directions with the performance curves under the condition of all the blades rotated at the same time, but have smaller offset and lower range of variation. When an individual blade angle error changes to +/- 2 degrees, the optimal efficiency of the mixed-flow pump will have no significant difference. When the individual blade angle error increases to +/- 4 degrees, the optimal efficiency will decrease by 1%.