Affiliation:
1. Research Center of Fluid Machinery Engineering and Technology, Jiangsu University, Zhenjiang 212013, China
2. Luoyang Institute of Science and Technology, School of Intelligent Manufacturing, Luoyang 471023, China
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.
Funder
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
Reference33 articles.
1. Simulation-based investigation of unsteady flow in near-hub region of a Kaplan Turbine with experimental comparison;Mulu;Eng. Appl. Comput. Fluid Mech.,2015
2. A novel energy losses dependence on integral swirl flow parameters in an elbow draft tube of a Kaplan turbine;Bozic;Renew. Energy,2021
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.
4. Exploration of the mechanism of cavitation vortex rope and vortex development in the draft tube of tubular turbine units;Cheng;Int. J. Agric. Biol. Eng.,2024
5. Vortex strip formation in a high head model Francis turbine;Goyal;J. Fluids Eng.,2017