Numerical Investigation of the Cavitation-Vortex Interaction Around a Twisted Hydrofoil with Emphasis on the Vortex Identification Method

Large eddy simulations combined with Zwart-Gerber-Belamri cavitation model is applied to investigate the physical interaction of the cavitation-vortex dynamics around a 3D twisted hydrofoil. The vortex structure of the hydrofoil surface at a typical instant is divided into three regions by the iso-surfaces of Ω method, i.e., the attach region-A, the shedding region-B and C. The results show that each region presents the different characteristic vortex structure, the attach region-A is primary and the secondary U-type vortex, the shedding region-B is O-shape vortex and 3D waves of the vortex structure, and the shedding region-C is the large-scale vortex structures. Then, the different vortex identification methods, namely, ω criterion, Q criterion, Ω method and Liutex method, is employed to capture vortex structures of unsteady cavitating flow. The 3D waves of the vortex structure and large-scale vortex structures are accurately captured with other vortex identification method, except for the ω criterion. It is noticeable that Liutex method can not only clearly display the U-type vortex structure, but also accurately describe its direction. The distribution of Liutex inside the primary U-type vortex structure is symmetric, and the head magnitude of U-type vortex is smaller than that of legs. The average magnitude of Liutex at the core is 1394.46. For the secondary U-type vortex structure, the magnitude of votex structure near the center of the hydrofoil is greater than that of the other side, and the average value is 738.1.