Analysis of Cavitation-Induced Unsteady Flow Conditions in Francis Turbines under High-Load Conditions

Hydraulic vibrations in Francis turbines caused by cavitation profoundly impact the overall hydraulic performance and operational stability. Therefore, to investigate the influence of cavitation phenomena under high-load conditions, a three-dimensional unsteady numerical simulation is carried out fo...

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Bibliographic Details
Published in:Processes 2024-01, Vol.12 (1), p.72
Main Authors: Wang, Haobo, Zhou, Daqing, Yu, An, Guo, Junxun
Format: Article
Language:English
Subjects:
Aerodynamics
Analysis
Cavitation
Draft tubes
Energy
Energy sources
Entropy
External pressure
Flow cavitation
Hydraulics
Hydroelectric power
Mathematical models
Numerical analysis
Optimization techniques
Simulation
Simulation methods
Turbines
Turbulence models
Two phase flow
Unsteady flow
Vibrations
Viscosity
Vortices
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Summary:Hydraulic vibrations in Francis turbines caused by cavitation profoundly impact the overall hydraulic performance and operational stability. Therefore, to investigate the influence of cavitation phenomena under high-load conditions, a three-dimensional unsteady numerical simulation is carried out for a Francis turbine with different head operating conditions, which is combined with the SST k-w turbulence model and two-phase flow cavitation model to capture the evolution of cavitation under high-load conditions. Additionally, utilizing entropy production theory, the hydraulic losses of the Francis turbine during cavitation development are assessed. Contrary to the pressure-drop method, the entropy production theory can quantitatively reflect the characteristics of the local hydraulic loss distribution, with a calculated error coefficient τ not exceeding 2%. The specific findings include: the primary sources of energy loss inside the turbine are the airfoil cavitation and cavitation vortex rope, constituting 26% and 71% of the total hydraulic losses, respectively. According to the comparison with model tests, the vapor volume fraction (VVF) inside the draft tube fluctuates periodically under high-load conditions, causing low-frequency pressure pulsation in the turbine’s power, flow rate, and other external characteristic parameters at 0.37 Hz, and the runner radial force fluctuates at a frequency of 1.85 Hz.
ISSN:2227-9717
2227-9717
DOI:10.3390/pr12010072