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Effect of modified draft tube with inclined conical diffuser on flow instabilities in Francis turbine

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  • Zhou, Xing
  • Shi, Changzheng
  • Miyagawa, Kazuyoshi
  • Wu, Hegao

Abstract

When a Francis turbine operates over an extended range of regimes far from the best efficiency point, the formation of a helical precessing vortex rope can lead to reduced efficiency, severe pressure fluctuations, and power swings. Because the existence of a vortex rope limits the operating range of the Francis turbine, it is necessary to adopt certain measures to mitigate the occurrence of vortex ropes and the associated pressure fluctuations, to improve the operating flexibility of the turbine. In the present study, a novel method to mitigate vortex ropes was proposed. This method involves using a modified draft tube with an inclined conical diffuser. Under the operating condition of a 16° Guide Vane Opening, four different inclination angles (from 0° to 24.4°) were investigated to determine the optimal inclination angle. Computational fluid dynamics results demonstrated that an inclination angle of 18.8° was the most effective for hindering the development of strong swirling flow and resulted in a decline in the pressure pulsation amplitude. This angle was later used under three other partial load operating points, and the results were compared with those of a traditional draft tube. The modified draft tube with an inclined conical diffuser exhibited satisfactory and stable performance in terms of reducing the flow instabilities within the draft tube. Based on an analysis of the mechanism for alleviation of the vortex rope, it was concluded that the inclined conical diffuser plays an effective role in reducing the swirling flow in the draft tube and thus destroying the development of the vortex rope. As a result, the proposed approach could be adopted to ameliorate the instability issue in Francis turbines.

Suggested Citation

  • Zhou, Xing & Shi, Changzheng & Miyagawa, Kazuyoshi & Wu, Hegao, 2021. "Effect of modified draft tube with inclined conical diffuser on flow instabilities in Francis turbine," Renewable Energy, Elsevier, vol. 172(C), pages 606-617.
    • Handle: RePEc:eee:renene:v:172:y:2021:i:c:p:606-617
    DOI: 10.1016/j.renene.2021.03.075
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    References listed on IDEAS

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    Cited by:

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    2. Zhou, Xing & Hu, Xinyi & Huang, Quanshui & Wu, Hegao & Tang, Xiaodan & Cervantes, Michel J., 2024. "Optimization design of an innovative francis draft tube: Insight into improving operational flexibility," Energy, Elsevier, vol. 299(C).
    3. Yang, Fan & Li, Zhongbin & Yuan, Yao & Lin, Zhikang & Zhou, Guangxin & Ji, Qingwei, 2022. "Study on vortex flow and pressure fluctuation in dustpan-shaped conduit of a low head axial-flow pump as turbine," Renewable Energy, Elsevier, vol. 196(C), pages 856-869.
    4. Shiraghaee, Shahab & Sundström, Joel & Raisee, Mehrdad & Cervantes, Michel J., 2024. "Extending the operating range of axial turbines with the protrusion of radially adjustable flat plates: An experimental investigation," Renewable Energy, Elsevier, vol. 225(C).
    5. He, Xianghui & Yang, Jiandong & Yang, Jiebin & Zhao, Zhigao & Hu, Jinhong & Peng, Tao, 2023. "Evolution mechanism of water column separation in pump turbine: Model experiment and occurrence criterion," Energy, Elsevier, vol. 265(C).
    6. Wang, Wen-Quan & Yu, Zhi-Feng & Yan, Yan & Wei, Xin-Yu, 2024. "Numerical investigation on vortex characteristics in a low-head Francis turbine operating of adjustable-speed at part load conditions," Energy, Elsevier, vol. 302(C).
    7. Zhou, Xing & Wu, Hegao & Cheng, Li & Huang, Quanshui & Shi, Changzheng, 2023. "A new draft tube shape optimisation methodology of introducing inclined conical diffuser in hydraulic turbine," Energy, Elsevier, vol. 265(C).
    8. Shahzer, Mohammad Abu & Kim, Jin-Hyuk, 2024. "Investigation of role of fins in a Francis turbine model's cavitation-induced instabilities under design and off-design conditions," Energy, Elsevier, vol. 292(C).

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