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| Transient start-up performance of mixed-flow pump and experimental study on visualization of cavitation flow field |
| ZOU Junjie1*, PAN Qiang2, ZHANG Desheng2 |
| 1. School of Marine Engineering, Jiangsu Shipping Vocational and Technical College, Nantong, Jiangsu 226010, China; 2. National Research Center of Pumps, Jiangsu University, Zhenjiang, Jiangsu 212013, China |
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Abstract The transient start-up characteristics and induced cavitation instability of mixed-flow pump are the urgent problems that should be solved in the development of pump-jet system and submarine weapon towards large-scale and stabilization. The transient start-up performance and cavitation flow field characteristics of a mixed-flow pump were studied by means of pump external characteristic test and high-speed photography visualization technology. The results show that the start-up duration and flow rate do not affect the pump performance at steady operating condition if there is no cavitation appears during the start-up process. The pump flow rate, speed and head reach the steady-state peak at the same time, which showing a good synchronicity under different starting conditions. However, the variation of pump head during the early stage of start-up lags behind the shaft speed and flow rate, and the retardation time of head is 50% of the start-up period at design flow rate. Under the condition of cavitation start-up, the cavitation inception first appears at the tip clearance of mixed-flow pump. With the increase of start-up time, the cavitation could develops into a ″long strip″ shape. With the decrease of inlet pressure or increase of inlet flow, the cavitation could gradually presents a triangle-shaped, and finally blocks the channel between impeller blades. Based on the evolution of cavitation morphology in the flow passage of mixed flow pump under different starting conditions is captured through high-speed photography experiment. It is found that shortening start-up duration, reducing the start-up flow rate and increasing start-up pressure at the pump inlet are the effective ways to suppress the occurrence of start-up cavitation.
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Received: 11 May 2021
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