LES investigation of cavitating flows around a sphere with special emphasis on the cavitation–vortex interactions

Abstract

Large eddy simulation (LES) was coupled with a homogeneous cavitation model to study turbulent cavitating flows around a sphere. The simulations are in good agreement with available experimental data and the simulated accuracy has been evaluated using the LES verification and validation method. Various cavitation numbers are simulated to study important flow characteristics in the sphere wake, e.g. periodic cavity growth/contraction, interactions between the cloud and sheet cavitations and the vortex structure evolution. The spectral characteristics of the wake for typical cloud cavitation conditions were classified as the periodic cavitation mode, high Strouhal number mode and low Strouhal number mode. Main frequency distributions in the wake were analyzed and different dominant flow structures were identified for each of the three modes. Further, the cavitation and vortex relationship was also studied, which is an important issue associated with complex cavitating sphere wakes. Three types of cavitating vortex structures alternate, which indicates that three different cavity shedding regimes may exist in the wake. Analysis of vorticity transport equation shows a significant vorticity increase at the cavitation closure region and in the vortex cavitation region. This study provides a physical perspective to further understand the flow mechanisms in cavitating sphere wakes. Three types of cavitating vortex structures alternate, i.e. the sub-scale vortex, fine vortex structure and large-scale vortex, are clearly discernible. The cavity shedding process produces the streamwise vortex cavitation, horseshoe-like shaped vortex cavitation and other complex vortex structures. This study provides a physical perspective to further understand the flow mechanisms in cavitating sphere wakes.