Exploration of the mechanism of cavitation vortex rope and vortex development in the draft tube of tubular turbine units
Keywords:
cavitation, vortex rope, vorticity transport equation, vortex line, draft tubeAbstract
Draft tube vortex rope is considered a special cavitation flow phenomenon in tubular turbine units. Cavitation vortex rope is one of the most detrimental factors affecting the safety of hydraulic turbines. In this study, ANSYS CFX software was utilized to numerically simulate the internal cavitation flow of a hydraulic turbine draft tube. The evolution of the cavitation vortex core was characterized by vortex line distribution and vorticity transport equation. The shape and number of blades influenced the revolving direction and distribution characteristics of the vortex close to the runner cone, which formed a counterclockwise-clockwise-counterclockwise distribution pattern. Simultaneously, there were many secondary flows in the draft tube. Mutual cancellation and dissipation between the flows was one of the reasons for reduction in vorticity. When the cross-sectional shape of the draft tube was changed, the vorticity was distributed from the center of the vortex rope to all parts of the cross-sectional draft tube, with extreme values at the center and at the walls. The vortex stretching and dilatation terms played a major role in the change in vorticity, with the baroclinic torque having an effect at the center of the vortex rope, this study is helpful to understand the flow of water in the draft tube and guide the design and optimization of the draft tube in engineering application. Keywords: cavitation, vortex rope, vorticity transport equation, vortex line, draft tube DOI: 10.25165/j.ijabe.20241701.8143 Citation: Cheng C, Li Z G, Shen C R, Gu S L, Zeng C C, Bai C Z, et al. Exploration of the mechanism of cavitation vortex rope and vortex development in the draft tube of tubular turbine units. Int J Agric & Biol Eng, 2024; 17(1): 163-171.References
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[2] Yao D, Ma B, Li Z G. A study on pressure fluctuation characteristics of bulb tubular turbine in a plant. China Rural Water and Hydropower, 2019; 12: 191–196, 199. (in Chinese)
[3] You Z. Bulb tubular power station. Beijing: China Water and Power Press, 2009; 419p. (in Chinese)
[4] Li W X, Li Z G, Qin Z, Yan S N, Wang Z, Peng S Y. Influence of the solution pH on the design of a hydro-mechanical magneto-hydraulic sealing device. Engineering Failure Analysis, 2022; 135: 106091.
[5] Zeng H J, Li Z G, Li D Y, Chen H, Li Z. Vortex distribution and energy loss in s-shaped region of pump turbine. Frontiers in Energy Research, 2022; 10: 904202;
[6] Min Z, Li Q T, Li Q F, Zhang Y P, Li Z G, Deng Y X. The analysis of the flow characteristic of draft tube based on cavitation flow of bulb turbine. China Rural Water and Hydropower, 2016; 1: 152–157. (in Chinese)
[7] Lu C, Chen L, Yao D. The test research for cavitation performance of bulb turbine under off-cam conditions. Mechanical & Electrical Technique of Hydropower Station, 2015; 38(6): 4–6, 17, 71.
[8] Peng S Y, Li Z G, Li X R, Chai X, Liu D Y, Zhao Y Z, et al. Flow analysis of tubular turbine draft tube based on vortex analysis. Engineering Journal of Wuhan University, 2020; 53(8): 679–685. (in Chinese)
[9] Kim S J, Suh J W, Choi Y S, Park J W, Park N H, Kim J H. Inter-blade vortex and vortex rope characteristics of a pump-turbine in turbine mode under low flow rate conditions. Water, 2019; 11(12): 2554.
[10] Ji B, Wang J, Luo X, Miyagawa K, Xiao L Z, Long X, et al. Numerical simulation of cavitation surge and vortical flows in a diffuser with swirling flow. Journal of Mechanical Science and Technology, 2016; 30(6): 2507–2514.
[11] Podnar A, Hočevar M, Novak L, Novak L, Dular M. Analysis of bulb turbine hydrofoil cavitation. Applied Sciences, 2021; 11(6): 2639.
[12] Huang R F, Ji B, Luo X W, Zhai Z H, Zhou J J. Numerical investigation of cavitation-vortex interaction in a mixed-flow waterjet pump. Journal of Mechanical Science and Technology, 2015; 29(9): 3707–3716.
[13] Sun L, Guo P, Luo X. Numerical investigation on inter-blade cavitation vortex in a Francis turbine. Renewable Energy, 2020; 158: 64–74.
[14] Sun L, Guo P, Luo X. Visualization investigation into processing vortex rope in Francis turbine draft tube based on several vortex identification criterions. Chinese Journal of Hydrodynamics, 2019; 34(6): 779–787. (in Chinese)
[15] Li D Y, Song Y C, Lin S, Wang H J, Qin Y L, Wei X Z. Effect mechanism of cavitation on the hump characteristic of a pump-turbine. Renewable Energy, 2021; 167: 369–383.
[16] Lu J. Investigation on the unsteady dynamic characteristics and its mechanism induced by cavitation in a centrifugal pump. PhD dissertation. Zhenjiang: Jiangsu University, 2017. (in Chinese)
[17] Zhang D, Zhang Q, Shi W. Basic theory and application of pump design CFD simulation. Beijing: China Machine Press, 2015. (in Chinese)
[18] Li Z G, Li W X, Wang Q F, Xiang R, Cheng J, Han W, et al. Effects of medium fluid cavitation on fluctuation characteristics of magnetic fluid seal interface in agricultural centrifugal pump. Int J Agric & Biol Eng, 2021; 14(6): 85–92.
[19] Li Z G. The research of combination relationship and performance of bulb tubular turbine. PhD dissertation. Lanzhou: Lanzhou University of Technology, 2014; 187p. (in Chinese)
[20] Li W X, Li Z G, Wang Z Y, Wu F, Xu L C, Peng S Y. Turbulence intensity characteristics of a magneto liquid seal interface in a liquid environment. Coatings, 2021; 11(11): 1333.
[21] Ruan H, Liao W L, Luo X Q, Zhao Y P, Qin H Z, Yang Z J. Effects of low pressure meridional position on cavitation performance for high-head pump-turbine. Transactions of the CSAE, 2016; 32(16): 73–81. (in Chinese)
[22] Cheng C, Li Z G, He F B, Wu S Y, Zeng C C, Zhang K, et al. Influence of Solid–Liquid Two-Phase Flow on Cavitation of Tubular Turbine Blades Under Combined Conditions. Frontiers in Energy Research, 2022; 10: 904201.
[23] Zhu G J, Li K, Feng J J, Luo X Q. Effects of cavitation on pressure fluctuation of draft tube and runner vibration in a Kaplan turbine. Transactions of the CSAE, 2021; 37(11): 40–49. (in Chinese)
[24] Li W X, Li Z G, Han W, Li Y B, Yan S N, Zhao Q, et al. Measured viscosity characteristics of Fe3O4 ferrofluid in magnetic and thermal fields. Physics of Fluids, 2023; 35(1): 012002.
[25] Tong B G, Yi X Y, Zhu K Q. Vortex motion theory. Hefei: University of Science and Technology of China Press, 2009; 256p. (in Chinese)
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Published
2024-03-31
How to Cite
Cheng, C., Li, Z., Shen, C., Gu, S., Zeng, C., Bai, C., … Hu, J. (2024). Exploration of the mechanism of cavitation vortex rope and vortex development in the draft tube of tubular turbine units. International Journal of Agricultural and Biological Engineering, 17(1), 163–171. Retrieved from https://ijabe.migration.pkpps03.publicknowledgeproject.org/index.php/ijabe/article/view/8143
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Power and Machinery Systems
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