Horizontal axis double-runner Francis turbines have great advantages in the development of small hydropower plants, but the arrangement of double runners aggravates the complexity of the water flow between runners, and the mutual influence of the two runners cannot be ignored. In order to explore the relationship between the performance and the internal flow field and investigate the pressure pulsation characteristics of the double-runner Francis turbine, the steady and unsteady numerical analysis of the full flow channel of a prototype turbine was carried out based on the Realizable k-epsilon model and the polyhedral mesh method. The results show that the relationship between the average efficiency of the two runners and the flow difference between the runners is negatively correlated. As the flow rate difference between the runners on both sides increases, the average efficiency of the runners decreases. The draft tube flow of a horizontal-axis turbine has a profound effect on the flow field characteristics in the runner. When the working conditions change, the turning and converging timing of the mainstream at the outlet of the two runners will change. The movement of the mainstream promotes the change in location of the dead water zone. The existence of the vortex zone makes the pressure distribution at the outlet of the runner uneven, which is an important reason for the asymmetry of the flow in the runner. The analysis of pressure pulsation and its frequency spectrum shows that when the working conditions change, the low-frequency, strong pressure pulsation area on the surface of the guide vane will regularly migrate between the two runners, while the high-frequency pressure pulsation that occurs in the bladeless zone will dissipate in the runner. The doubling of the blade frequency on the pressure surface and back surface of the blades gradually attenuates with the increase of frequency. The pressure pulsation attenuation on the surface of the high-position blade conforms to the linear law, and the attenuation of the pressure pulsation on the surface of the low-position blade conforms to the exponential law. The research in this paper provides a certain reference value for revealing the flow field mechanism and pressure pulsation characteristics of the double-runner Francis turbine.
The self-priming transient process and stable state in the irrigation self-priming pump typed 65ZB-40C was simulated by CFD method. The transient process and steady state was compared, and the characteristics of energy conversion within impeller were demonstrated from aspects of working process and energy loss process. Under different operating conditions, the inner flow characteristics were demonstrated in the power, distribution of power density and turbulence dissipation rate. The results indicated that obvious differences existed between the transient and steady state. The work done by the surface pressure in the flow passage is the main driving power to the impeller. The power increased with the enlargement of the radius of the impeller, which increased rapidly in the inlet region of the impeller, and increased slightly in the middle and outlet region of the impeller. Under the small flow conditions, the region of large turbulence dissipation rate expanded obviously. Under the large flow conditions, the turbulence dissipation rate increased in the flow passage near the tongue. At the time when the self-priming began to prime for 20 seconds, in the middle and outlet region, the large turbulence dissipation rate appeared.1. Introduction Self-priming pump is a kind of special centrifugal pump,that it doesn't need be filled fully with water at the beginning. After a short time of operating, air can be expelled spontaneously and water is sucked by pump itself for normal operation. Self-priming pump is widely used in irrigation and drainage, construction, mine drainage, city fire fighting, Military, petrochemical industry, food industry and so on. But the self-priming pump produced in china existed some problems such as complex structure, large size, difficulty of being casted, low suction height, long self-priming time etc.[1-2].Many scholars had done many experiments research of the influences of the hydraulic structural parameters the self-absorption properties of self-priming pump. They concluded some of the relationships among the factors and the rules of the design, but the design methods of the self-priming pump have still stayed in the semi-empirical theories stage, which cannot meet the demand of predicting properties and the requirement of new products design. In order to know the flow rule, it becomes very important to research the inner flow of the self-priming pump [3].Self-priming pump have both the features of the ordinary centrifugal pump and self-priming pump The largest self-priming height and self-priming time under the largest self-priming height are primary evaluating indicators for the self-priming pump. The performance of self-priming and steady state of self-priming pump were shown by applying the CFD.
Based on the design methods of fish friendly hydraulic turbines at home and abroad and traditional hydraulic turbines, this paper designs an axial flow fish friendly hydraulic turbine in plateau area by using Unigraphics NX. The steady-state simulation of the turbine is carried out by fluent, and the energy characteristics of the three blade runner are analyzed. Through the transient computation, the pressure fluctuation characteristics in the leafless area of the turbine with guide vane opening of 18.2° and 14.2° are studied, and the fish passing characteristics are analyzed. Compared with the evaluation criteria of fish friendly water turbine, the variation rate of pressure obtained is less than 550.3kpa/s, which meets the design criteria of fish friendly water turbine and basically meets the demand of fish passing down the dam.
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