Abstract
The flow losses owing to friction and unstable flow patterns in Francis turbines will cause a drop in their efficiency. The traditional approach to evaluating the hydraulic losses of Francis turbine via the pressure drop cannot determine the exact locations at which the high energy loss occurs. In this paper, a full analysis for flow losses in a Francis turbine with the entropy production method has been implemented. Firstly, the prediction of hydraulic efficiency between entropy production theory and the model test is compared. Secondly, distribution of entropy production in different parts and flow components is analyzed. Finally, detailed distribution of local entropy production rate (LEPR) in spiral casing, stay/guide vanes, runner and draft tube is investigated. It is found that hydraulic losses of the turbine are closely related to flow separation and the vortex motion as well as backflow. Meanwhile, draft tube accounts for the greatest proportion of entropy production followed by the runner. It is concluded that the entropy production method adopted in this paper can be feasible to explore where the energy dissipation happens and how it is distributed in Francis turbine passage under different operating conditions within a certain reasonable range of error.
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