Analysis of flow field in draft tube of pump-turbine during load increasing period
Li Rennian1, Jiang Lei1, Li Qifei1, Han Wei1, Liu Baofu2
1.School of Energy and Power Engineering, Lanzhou University of Technology, Lanzhou, Gansu 730050, China; 2.Qinghai Engineering Construction Branch Office, Yellow River Upstream Hydropower Development Co. Ltd., Xining, Qinhai 810008, China
To study the internal transient flow characteristics of the draft tube in a pump-turbine during its load increasing period, the unsteady fluid flow in the pump-turbine is simulated based on the dynamic mesh method in Fluent. According to the simulated results, the transient evolution of flow structure in the draft tube is analyzed extensively. The results show that the relationships of pressure with time are basically similar in the cone and elbow during the period. A sudden increase and remarked fluctuation in static pressure just occurs at the first period of time(0-0.9 s)during the wicket gate opening starting to change. After 0.9 s, the averaged fluctuation in the static pressure is not beyond 9.76 kPa, showing the static pressure remains constant roughly. Besides, a notable vortex rope and a reverse flow structure exist in the draft tube in smaller wicket gate openings, which can easily lead to the instability in operation of the pump-turbine. With the increasing wicket gate opening, the flow in the draft tube becomes steady gradually, suggesting the increase of flow rate can make the flow in the draft tube smoother.
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