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| Influence of abnormally low head on pressure fluctuation of pump turbine |
| LI Qifei, TAN Haiyan, LI Rennian, JIANG Lei, LYU Wenjuan |
| College of Energy and Power Engineering, Lanzhou University of Technology, Lanzhou, Gansu 730050, China |
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Abstract In order to study the pressure fluctuation characteristics of a pump turbine under the abnormally low head, Realizable k-ε turbulence model is used to simulate the unsteady flow of four opera-ting points. The pressure signals of the four monitoring points,i.e. in the inlet of spiral casing, after the guide vanes and before the runner, in the upstream of the draft tube cone and inside the draft tube elbow, are achieved and compared with the experimental results. And then, the pressure signals under the operating condition a0=37 mm and Q11=0.865 m3/s are analyzed in the time domain and frequency domain respectively. It is concluded that Realizable k-ε turbulence model can accurately si-mulate the pressure fluctuation in the larger guide opening of pump turbine. The pressure fluctuation of the inlet of the spiral casing is relatively disorder. When the unit is just open, the pressure fluctuation value is relatively great. The main frequency of pressure fluctuation in the inlet of the spiral casing is 19.78 Hz, equal to the rotational frequency,showing that in this condition, the pressure fluctuation in the inlet of spiral casing of the pump turbine is influenced by the rotating of the runner in the downstream. Because the pressure fluctuation in the vaneless space between the guide vane and the runner is affected by the static and dynamic interference, its change is periodic and main frequency is equal to the blade passing frequency. Owing to the internal flow and the vortex strip in the draft tube, the pressure fluctuation in the draft tube is a low-frequency fluctuation and its main frequency is 0.35 times the frequency of the runner passing through.
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Received: 25 December 2014
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