Consideration of prediction methods for cavitation surge using 1D-3D coupling analysis

Cavitation surge may occur in the draft tube of a hydro turbine under overload conditions. As a prediction method, we proposed the method combining one-dimensional analysis and CFD (hereinafter referred to as “1D-3D coupled analysis”). We compared the results of experiments using a test apparatus incorporating the venturi tube with the results of conventional analysis methods using CFD alone and 1D-3D coupled analysis. The results confirmed changes in the oscillation amplitude and frequency of cavitation volume through 1D-3D coupled analysis. The moment when the cavitation volume became zero, which was observed in the conventional analysis, was improved by 1D-3D coupled analysis, but it was found that this was due to the boundary conditions. However, the influence of the one-dimensional model was observed in terms of oscillation frequency of the cavitation volume. Among the factors influenced by the one-dimensional model, the mass and compliance of the tanks were considered, but analytical examination revealed that the effect of compliance was dominant.