Influences of Rotational Speed Variations on the Flow-Induced Vibrational Performance of a Prototype Reversible Pump Turbine in Spin-No-Load Mode

Abstract

During the spin-no-load mode, vibrational performance of the reversible pump turbine is an important criterion for the evaluation of the operational performances of the power station. In the present paper, the influences of rotational speed variations on the vibrational performances of the whole unit (including the top cover, the upper, and the lower brackets) are experimentally investigated with discussions of their sources and propagation characteristics. According to the whole vibrational levels and the dominant frequencies of the vibration signals obtained at the top cover, the investigated cases with different rotational speeds could be divided into three partitions with their main characteristics given as follows. In the first partition (with low rotational speeds), the vibrational level is quite limited, and its source is the pressure fluctuation generated by the swirling vortex rope in the draft tube. In the second partition (with medium rotational speeds), the vibrational level gradually increases and its source is the mechanical aspects of the impeller rotation. In the third partition (with high rotational speeds), the vibrational level is prominent with a prominent swirling vortex rope in the draft tube and intensive rotor–stator interactions in the vaneless space (VS). For the vibrations of the upper and the lower brackets, the vibrations mainly originate from the mechanical aspects of the impeller rotation and the amplitudes of the dominant frequency also increase with the increment of the rotational speed. Finally, differences between the vibrational performances of the spin-no-load mode and the generating mode are discussed.