Influence of Runner Downstream Structure on the Flow Field in the Draft Tube of a Small-Sized Water Turbine
Source abstract
Abstract
The flow in the draft tube of the water turbine is affected by the upstream flow and the inherent structure accompanied by various undesirable characteristics, affecting the efficient and stable operation of the water turbine. Changing the flow structure downstream of the runner is an important measure to reduce hydraulic loss in the draft tube and improve stability. In this study, three downstream structures of the runner, namely, the non-locking nut, small locking nut, and extended locking nut are numerically calculated and verified using experimental results. The unstable flow characteristics of the draft tube are analyzed using variations in swirling flow, backflow, pressure gradient, and vortex strip. The results show the non-negligible effect of the locking nut, which significantly reduces the rotational momentum flux at the draft tube inlet, accelerates the decay rate of the swirling flow, and suppresses the generation of axial low pressure. The small locking nut significantly reduces the pressure gradient, shortens the backflow zone, and decreases the backflow velocity. The extended locking nut reduces the backflow zone in some sections and reduces the vortex zone of the straight section but prolongs the backflow zone and increases the backflow velocity.
Source: crossref · Quality: baseline
Research context
OpenAlex topics: Cavitation Phenomena in Pumps · Fluid dynamics and aerodynamics studies · Cyclone Separators and Fluid Dynamics
SciVX discovery tags are terminology-based. OpenAlex topics are source-provided classifications.
Affiliations
Research Center of Fluid Machinery Engineering and Technology, Jiangsu University, Zhenjiang 212013, China
Luoyang Institute of Science and Technology, School of Intelligent Manufacturing, Luoyang 471023, China
Funding
National Natural Science Foundation of China · Jiangsu Association for Science and Technology Young Science and Technology Talent Support Project · National Key Research and Development Program of China · Scientific and Technological Breakthrough Foundation of Henan Province
References (33)
Show source-provided references
1. Simulation-based investigation of unsteady flow in near-hub region of a Kaplan Turbine with experimental comparison
2. A novel energy losses dependence on integral swirl flow parameters in an elbow draft tube of a Kaplan turbine10.1016/j.renene.2021.05.014 ↗
3. Ji, L., Xu, L., Peng, Y., Zhao, X., Li, Z., Tang, W., Liu, D., and Liu, X. (2022). Experimental and Numerical Simulation Study on the Flow Characteristics of the Draft Tube in Francis Turbine. Machines, 10.10.3390/machines10040230 ↗
4. Exploration of the mechanism of cavitation vortex rope and vortex development in the draft tube of tubular turbine units
5. Vortex strip formation in a high head model Francis turbine10.1115/1.4035224 ↗
6. A method of evaluating the vortex rope strength in draft tube of Francis turbine10.1016/j.renene.2020.01.020 ↗
7. Numerical investigation of air admission influence on the precessing vortex strip in a Francis turbine
8. Vortex core formation in a Francis turbine during transient operation from best efficiency point to high load10.1063/5.0012227 ↗
9. Influence of swirling flow parameters on frequency response of a simplified draft-tube in presence of cavitation10.1016/j.ijheatfluidflow.2022.109043 ↗
10. Numerical and experimental investigation of the effect of baffles on flow instabilities in a Francis turbine draft tube under partial load conditions10.1177/1687814018824468 ↗
11. Suppression of vortex strip oscillation and pressure vibrations in Francis turbine draft tube using various strategies10.1007/s42241-021-0038-4 ↗
12. Investigation of cavitating vortex strip instabilities and its suppression inside a Francis turbine model with Thoma number variation10.1063/5.0140973 ↗
13. Kim, S.-J., Choi, Y.-S., Cho, Y., Choi, J.-W., Hyun, J.-J., Joo, W.-G., and Kim, J.-H. (2020). Effect of fins on the internal flow characteristics in the draft tube of a francis turbine model. Energies, 13.10.3390/en13112806 ↗
14. Suppression of vortex strip formation and pressure fluctuation using anti-swirl fins in a Francis turbine model at part load condition with cavitation inception point10.1063/5.0097685 ↗
15. Mitigation of swirling flow with a vortex strip by passive installations—Theory, simulations, and experiments10.1063/5.0128029 ↗
16. The effect of runner cone design on pressure oscillation characteristics in a Francis hydraulic turbine10.1177/0957650911422865 ↗
17. Influence of runner cone profile and axial water jet injection in a low head Francis turbine at part load
18. Runner cone optimization to reduce vortex strip-induced pressure fluctuations in a Francis turbine10.1007/s11431-021-1867-2 ↗
19. The influence of runner cone perforation on the draft tube vortex in Francis hydro-turbine10.2298/TSCI171011040S ↗
20. Runner cone drilling and slotting to reduce vortex strip—Induced pressure fluctuations in a Francis turbine10.1177/09576509231178387 ↗
21. Lučin, I., Sikirica, A., Kuliš, M., and Čarija, Z. (2022). Investigation of Efficient Optimization Approach to the Modernization of Francis Turbine Draft Tube Geometry. Mathematics, 10.10.3390/math10214050 ↗
22. Favrel, A., Lee, N.-J., Irie, T., and Miyagawa, K. (2021). Design of experiments applied to Francis turbine draft tube to minimize pressure pulsations and energy losses in off-design conditions. Energies, 14.10.3390/en14133894 ↗
23. An analysis of the impact of draft tube modifications on the performance of a Kaplan turbine by means of computational fluid dynamics10.1177/0954406217713520 ↗
24. A new draft tube shape optimisation methodology of introducing inclined conical diffuser in hydraulic turbine10.1016/j.energy.2022.126374 ↗
25. Effect of modified draft tube with inclined conical diffuser on flow instabilities in Francis turbine10.1016/j.renene.2021.03.075 ↗
26. Szakal, R.-A., Doman, A., and Muntean, S. (2021). Influence of the reshaped elbow on the unsteady pressure field in a simplified geometry of the draft tube. Energies, 14.10.3390/en14051393 ↗
27. Francis turbine draft tube parameterization and analysis of performance characteristics using CFD techniques10.1016/j.renene.2018.04.055 ↗
28. CFD study on prediction of vortex shedding in draft tube of Francis turbine and vortex control techniques10.1016/j.renene.2015.09.041 ↗
29. Study on suppression of cavitating vortex rope on pump-turbines by J-groove10.1016/j.apenergy.2024.122843 ↗
30. Skripkin, S., Zuo, Z., Tsoy, M., Kuibin, P., and Liu, S. (2022). Oscillation of cavitating vortices in draft tubes of a simplified model turbine and a model pump-turbine. Energies, 15.10.3390/en15082965 ↗
31. On the generation mechanisms of low-frequency synchronous pressure pulsations in a simplified draft-tube cone10.1016/j.ijheatfluidflow.2021.108912 ↗
32. Flow in the simplified draft tube of a francis turbine operating at partial load-part I: Simulation of the vortex strip10.1115/1.4026817 ↗
33. Effects of Vortex Structure on Hydraulic Loss in a Low Head Francis Turbine under Overall Operating Conditions Base on Entropy Production Method10.1016/j.renene.2022.08.084 ↗