Experiment on the influence of self-draining partition pier on the performance of axial flow pump
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Abstract:
Large low-head pumping stations are widely constructed in the Yangtze River Delta, situated along both rivers and lakes. These stations are an important part of China's pumping station project, operating under low head, with large flow capacities and a high degree of automation. Due to its long and changeable inlet and outlet channels, the key to reduce the hydraulic loss in their channels was to improve the operation efficiency of drainage pumping stations . At present, due to terrain and other reasons, many low-head drainage pumping stations behind levees set up long dike box culverts as self-discharging channels. When large low-head drainage pumping stations with long self-discharging channels operate under pumping conditions, part of the water flowing from the rear side of the horn into the horn will rotate at low speed in the self-discharging channel behind the inlet channel to form a return zone, which exacerbates the vortex band and affect the performance of the device. Chenying pumping station was took as the research object to explore the improvement measures for the performance of the vertical axial flow pump with a long self-draining channel, with the partition pier set in the self-draining channel and a comparative study on the model test was conducted. The actual operation of the device could be accurately analyzed and the design scheme suitable for the pumping station was optimized based on the results of the model test of the pump device. Combining the results of the comparison between the original scheme and the optimized scheme, the targeted rectification optimization scheme was provided for the pumping station. The results indicated that the efficiency increased slightly in the full head range of the device after setting the partition pier and the device efficiency increased from 71.9% to 73.0% under the design head condition when the critical cavitation margin decreased from 8.7 m to 8.2 m. The addition of partition pier had little influence on the runaway performance of the device at various angles and the runaway speed corresponding to the maximum head of the device was 518.53 r/min, which was equal to 1.73 times of the rated speed, meeting the requirements of safe operation of the pump. The amplitude value of pressure pulsation of the horn inlet at different angles became smaller and more stable under large flow condition, and the amplitude value and average peak value of real-time water pressure pulsation also showed a decrease when the device operated under the design angle condition. Additionally, the amplitude of pressure pulsation and the D-value between the extreme amplitude of pressure pulsation at the horn inlet of the device in the large flow range of 364 to 426 L/s gradually decreased after the addition of partition pier. When the device operated under the design angle condition, both the high and low frequency signals on the spectrum of the corresponding two monitoring points were significantly reduced and the main frequency became multiples of the blade frequency, with the amplitude of various sub-harmonic frequencies decreased. The results showed that in a large low-head pumping station with an extended self-draining channel, adding a partition pier could eliminate the vortex zone. This change allowed water near the horn to flow into it more smoothly, resulting in a more stable flow field in the inlet channel. The addition of the partition pier significantly improved the energy, cavitation and pressure pulsation characteristics of the device, particularly enhancing its cavitation performance under low head and high flow conditions.
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