To predict unstable characteristic

To predict unstable characteristic of mixed flow pump, two mixed flow pumps were experimentally and numerically investigated. Calculated characteristics agreed well with experimental ones. It was clarified from the numerical results that stall mechanism was different between two impellers. One was the blade stall induced by separation on the suction surface of impeller. The other was wall stall induced by separation on the casing wall. Two stall indices were also proposed from the numerical results. The diffusion factor was the index indicating the inception point of the blade stall. The Taylor's pressure coefficient was the index indicating the inception point of the wall stall. The critical values of those indices for the two pumps investigated in this study were derived from the calculation results and agreed well with those values derived from the experimental results.