Applying coupled simulation of 1D model and CFD for unstable cavitation flow in venturi tube

Abstract

The swirling flow with cavitation can cause the cavitation volume fluctuation in a draft tube of a hydro turbine at the full load operating conditions, causing pressure pulsations with flow rate fluctuations known as cavitation surge throughout the hydraulic system. The cases that predicted the phenomenon qualitatively using the CFD analysis have been reported previously, whereas the methods to predict the cavitation volume and the fluctuation frequency in the cavitation surge condition quantitatively have not yet been established. Therefore, in this study, the influence of the boundary conditions on the prediction accuracy of the cavitation surge was investigated in CFD analysis. The frequency of the cavitation surge was calculated to be lower than the experimental results because cavitation surge causes flow fluctuation throughout the hydraulic system, but only part of the hydraulic system was modeled and the boundary condition was fixed in CFD analysis. These results imply that the entire hydraulic system must be modeled to improve prediction accuracy. Thus, in this study, the entire system was modeled in 1D and coupled with CFD. This coupled simulation improved the prediction accuracy of the frequency, and the effectiveness of the coupled simulation considering the entire hydraulic system was clarified.