ICCM Conferences, The 12th International Conference on Computational Methods (ICCM2021)

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Entropy production analysis of energy loss of a Francis turbine under overall operating conditions: hybrid RANS/LES simulations
Zhi-Feng Yu

Last modified: 2021-06-14


The flow losses owing to friction and unstable flow patterns in Francis turbines will cause a drop in its efficiency. Traditional efficiency evaluating method via total pressure loss is incapable of locating the exact position of the losses. A method of entropy production with high sensitivity at energy losses has attracted much attention, but few give attention to its applications to Francis turbine. In this paper, unsteady numerical calculation via high-fidelity Delayed Detached Eddy Simulation (DDES) is conducted, and the energy loss in a Francis turbine under overall operating conditions is evaluated using entropy production method. First, the accuracy of entropy production method is validated by experimental results obtained from the model test. Second, the variations in the entropy production of different parts and flow components are analyzed. Finally, detailed distribution of local entropy production rate (LEPR) and flow characteristics in each flow component (spiral casing, stay/guide vanes, runner, and draft tube) is investigated. It is found that flow losses in Francis turbine are closely related to flow separation, vortex motion, and secondary flow. And the viscous dissipation losses are slightly greater than that of the turbulence dissipation losses for all turbine cases. Moreover, draft tube accounts for the greatest proportion of entropy production, while the entropy production in the spiral casing and stay/guide vanes is the least. It is believed that the key reason why great energy dissipation is caused in the draft tube of Francis turbine is that the vortex rope is transporting continuously towards the downstream, especially when the turbine is deviating from optimum operating point.

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