Investigations of the thermodynamic entropy evaluation in a hydraulic turbine under various operating conditions

Abstract

The irreversible energy loss due to viscous and turbulent dissipation in a Francis turbine led to a decrease in efficiency. It is difficult to reveal the detailed energy loss distribution by either experimental method or traditional simulation method. In this investigation, the entropy production method is applied to calculate the irreversible energy loss quantitatively and demonstrate the spatial distribution of energy loss intuitively. The flow in the Francis turbine is numerically simulated based on SST turbulence model and Zwart cavitation model. The objectives of this study are to (1) verify the accuracy of entropy production method in irreversible energy loss calculation, (2) investigate the detailed characteristics of entropy production rate in blade channel, blade surface and draft tube, (3) reveal the internal interaction mechanism between cavitation process and entropy production rate generation. The results show that the entropy production method has a credible accuracy for irreversible energy loss calculation. Draft tube and runner have the maximum amount of energy loss, but the guide vanes and runner have the maximum ability of irreversible energy loss generation. Finally, the new definition of entropy production rate induced by cavitation is derived to reveal the interaction mechanism between cavitation process and entropy production rate.