We predicted the leakage flow rates of a pressure seal in an actual high-pressure multistage pump. Since the pressure of the actual pump is higher than that of a model pump, accurate prediction of leakage flow rate and rotor dynamic forces for an actual pump is more difficult than that for a model pump. A non-contacting seal is used as a pressure seal to suppress leakage flow for high-pressure multistage pumps. When such pumps are operated at high speed, the fluid force acting on an eccentric rotor may cause vibration instability. For vibration stability analysis, we need to estimate static and dynamic characteristics of the pressure seals, i.e., leakage flow rate and rotor dynamic coefficients. We calculated the characteristics of the pressure seal based on Iwatsubo group’s method. The pressure seal we developed has labyrinth geometry consisting of grooves with different sizes. This method numerically calculates the characteristics of the grooved seal by using a three-control-volume model and a perturbation method. We compared the calculated and measured leakage flow rates. We found that the calculated results quantitatively agreed with the measured one in the actual pump and the characteristics of pressure and velocity for the seal with non-uniform-sized grooves were clarified.

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