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Investigation of Rotating Vortex Rope formation during load variation in a Francis turbine draft tube

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  • Sotoudeh, Nahale
  • Maddahian, Reza
  • Cervantes, Michel J.

Abstract

Rotating Vortex Rope (RVR) has been a matter of focus for years due to the major effects on hydraulic turbine’s efficiency. The exact procedure of RVR formation is still vague. The present research focuses on the dynamics of the RVR formation during the load variation employing transient numerical simulations. Two different geometries including the full geometry and the reduced one, which consists of one stay vane, two guide vanes, one runner blade, one splitter blade and full draft tube, are considered. In order to capture the transient swirling flow features inside the draft tube, the Shear Stress Transport-Scale Adaptive Simulation (SST-SAS) model is utilized to approximate the turbulent stresses. The pressure results inside the draft tube agree well with the experimental measurements. Moreover, the velocity results show the central low-axial-velocity and high-tangential-velocity region in the draft tube properly. The flow structure is visualized using λ2 criterion. The dynamic of RVR and the physics behind the RVR formation are investigated during the load variation. The results indicate four flow regimes with different characteristics during RVR formation. The first flow regime is a stable swirling structure occurring at Best Efficiency Point (BEP). The second flow regime occurs at the beginning of the load variation where signs of flow instabilities appear. These instabilities are temporary and washed down by the upstream flow. Expanding the instabilities and creating the vortical structures in the draft tube are the important flow features in the third flow regime. The fourth flow regime is the presence of a developed rotating rope occurring at the Part Load (PL) condition. The flow regimes differ according to the size and shape of the stalled region during load rejection inside the draft tube cone. They also reveal that despite some shortcomings, the reduced model is reliable to simulate the RVR transient formation. The full geometry simulations could be also applicable for practical problems provided that the modified time step is slightly greater than the main blade rotational angle is used.

Suggested Citation

  • Sotoudeh, Nahale & Maddahian, Reza & Cervantes, Michel J., 2020. "Investigation of Rotating Vortex Rope formation during load variation in a Francis turbine draft tube," Renewable Energy, Elsevier, vol. 151(C), pages 238-254.
    • Handle: RePEc:eee:renene:v:151:y:2020:i:c:p:238-254
    DOI: 10.1016/j.renene.2019.11.014
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    References listed on IDEAS

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    1. Chirag Trivedi & Michel J. Cervantes & B. K. Gandhi, 2016. "Investigation of a High Head Francis Turbine at Runaway Operating Conditions," Energies, MDPI, vol. 9(3), pages 1-22, March.
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    6. Laouari, Ahmed & Ghenaiet, Adel, 2019. "Predicting unsteady behavior of a small francis turbine at several operating points," Renewable Energy, Elsevier, vol. 133(C), pages 712-724.
    7. Trivedi, Chirag & Agnalt, Einar & Dahlhaug, Ole Gunnar, 2017. "Investigations of unsteady pressure loading in a Francis turbine during variable-speed operation," Renewable Energy, Elsevier, vol. 113(C), pages 397-410.
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    1. Zhumei Luo & Cong Nie & Shunli Lv & Tao Guo & Suoming Gao, 2022. "The Effect of J-Groove on Vortex Suppression and Energy Dissipation in a Draft Tube of Francis Turbine," Energies, MDPI, vol. 15(5), pages 1-20, February.
    2. Binama, Maxime & Kan, Kan & Chen, Hui-Xiang & Zheng, Yuan & Zhou, Daqing & Su, Wen-Tao & Muhirwa, Alexis & Ntayomba, James, 2021. "Flow instability transferability characteristics within a reversible pump turbine (RPT) under large guide vane opening (GVO)," Renewable Energy, Elsevier, vol. 179(C), pages 285-307.
    3. Kumar, Sandeep & Cervantes, Michel J. & Gandhi, Bhupendra K., 2021. "Rotating vortex rope formation and mitigation in draft tube of hydro turbines – A review from experimental perspective," Renewable and Sustainable Energy Reviews, Elsevier, vol. 136(C).
    4. Rafel Roig & Xavier Sánchez-Botello & Xavier Escaler & Berhanu Mulu & Carl-Maikel Högström, 2022. "On the Rotating Vortex Rope and Its Induced Structural Response in a Kaplan Turbine Model," Energies, MDPI, vol. 15(17), pages 1-19, August.
    5. Lei, Liuwei & Li, Feng & Xu, Beibei & Egusquiza, Mònica & Luo, Xingqi & Zhang, Junzhi & Egusquiza, Eduard & Chen, Diyi & Jiang, Wei & Patelli, Edoardo, 2022. "Time-frequency domain characteristics analysis of a hydro-turbine governor system considering vortex rope excitation," Renewable Energy, Elsevier, vol. 183(C), pages 172-187.
    6. Kim, Seung-Jun & Yang, Hyeon-Mo & Park, Jungwan & Kim, Jin-Hyuk, 2022. "Investigation of internal flow characteristics by a Thoma number in the turbine mode of a Pump–Turbine model under high flow rate," Renewable Energy, Elsevier, vol. 199(C), pages 445-461.
    7. Ivan Litvinov & Daniil Suslov & Evgeny Gorelikov & Sergey Shtork, 2021. "Experimental Study of Transient Flow Regimes in a Model Hydroturbine Draft Tube," Energies, MDPI, vol. 14(5), pages 1-13, February.
    8. Raluca Gabriela Iovănel & Arash Soltani Dehkharqani & Diana Maria Bucur & Michel Jose Cervantes, 2022. "Numerical Simulation and Experimental Validation of a Kaplan Prototype Turbine Operating on a Cam Curve," Energies, MDPI, vol. 15(11), pages 1-24, June.
    9. Salehi, Saeed & Nilsson, Håkan, 2022. "Flow-induced pulsations in Francis turbines during startup - A consequence of an intermittent energy system," Renewable Energy, Elsevier, vol. 188(C), pages 1166-1183.
    10. Salehi, Saeed & Nilsson, Håkan, 2022. "Effects of uncertainties in positioning of PIV plane on validation of CFD results of a high-head Francis turbine model," Renewable Energy, Elsevier, vol. 193(C), pages 57-75.
    11. Salehi, Saeed & Nilsson, Håkan & Lillberg, Eric & Edh, Nicolas, 2021. "An in-depth numerical analysis of transient flow field in a Francis turbine during shutdown," Renewable Energy, Elsevier, vol. 179(C), pages 2322-2347.
    12. Su, Wen-Tao & Binama, Maxime & Li, Yang & Zhao, Yue, 2020. "Study on the method of reducing the pressure fluctuation of hydraulic turbine by optimizing the draft tube pressure distribution," Renewable Energy, Elsevier, vol. 162(C), pages 550-560.

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