In order to study the transient characteristics of centrifugal pump as turbine (PAT) in the process of startup, UDF programs were written according to the rotation equations. Rotational speed control method based on Fluent sliding mesh was used to carry out numerical simulation of PAT during startup process, which was compared with the experimental results. The results show that strong leaf vortices are formed within the impeller at the initial time of startup, besides, the intensity of blade vortex decreases gradually and the pressure assumes gradient distribution with the increase of rotational speed. Blade load shows oscillatory distribution at the initial time of startup, and its maximum amplitude appears in the middle of the blade position, which is much higher than blade load of steady state condition. Radial force and axial force both increase sharply with the increase of rotational speed but decrease oscillatorily soon afterwards. After the rotational speed intends to be stable, radial force and axial force assume periodic oscillation. Pulse amplitude of axial force is less than that of radial force, and each pulse frequency of the oscillation period is consistent with leaf number. The acceleration of rotor decreases gradually in the process of startup, moreover, the greater pressure of flow fluid is, the shorter time is to meet the design speed, and the higher the steady speed is after completion of startup. The smaller the moment of inertia is, the faster startup is completed.
Key words
pump as turbine /
startup process /
rotational speed /
transient characteristic
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References
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