Application of Liutex and Entropy Production to Analyze the Influence of Vortex Rope in the Francis-99 Turbine Draft Tube

The vortex structures in a draft tube of a Francis turbine are confused, primarily when cavitation occurs, which may induce severe vibration and noise. Understanding this vortex's periodical precession and investigating the vortex rope influence in the draft tube cone is required for stable operation at off-design conditions. This study captured the cavitating flow with high accuracy by utilizing the SST turbulence and ZGB cavitation models. The Omega and Liutex methods are employed and compared with the traditional Q -criterion to determine the vortex rope behavior in the Francis-99 turbine draft tube. The result showed that the Liutex/Rortex method is advantageous over the Q -criterion for representing the vortex rope structure. The Liutex method can effectively remove the boundary layer's influence on visual vortex structures from the draft tube's wall. Moreover, the local hydraulic loss distribution was clarified by using entropy production. By comparing Liutex magnitude distribution and entropy production rate, the vortex rope behavior effects on local hydraulic loss were significantly illuminated.