Numerical analysis of the influence of the non-uniform inflow induced by streamwise vortices on the cavitating flow around hydrofoil

Abstract

Cavitation under non-uniform inflows is a commonly encountered situation in engineering applications. In the present study, the effects of the streamwise vortices on cavitating flows are investigated separately, which are extracted from the non-uniform inflow of some non-straight inlet casings of condensate pumps. The unsteady cavitating flow around NACA66 hydrofoils with Vortex Generators (VGs) installed upstream (VGs-Up and VGs-Down), as well as a single NACA66 without VGs (benchmark case), is numerically analyzed. The Large Eddy Simulation (LES) coupled with a homogeneous cavitation model is employed to capture complex cavitating flow structures. The influences of the streamwise vortices induced by the vortex generators (SV_VGs) on partial cavitation are analyzed by comparing the three cases. The results show that the SV_VGs tend to intensify the cavitation degree around the foil for both VGs-Up and VGs-Down, and they will generate a noticeable concave trace on the cavities. However, the different positions of the SV_VGs appear to have little influence on pressure distribution, as well as lift and drag forces change in cavitating flow. During the whole cavity shedding cycle, three types of interaction mechanisms between SV_VGs and cavitating flow field are analyzed: 1) SV_VGs-Sheet Cavity interaction; 2) SV_VGs-Vortex interaction; 3) SV_VGs-Cloud Cavity interaction. As for the vorticity field, influenced by the SV_VGs, the vorticity transport process assumes 3D characteristics. Further analysis of the mean cavitating flow field reveals that the streamwise vortices in the free stream mainly contribute to the first half of the sheet cavities, whereas having little impact on the second half of the cloud cavities due to the rapid attenuation of their vorticity strength. In addition, the upstream streamwise vortices in the free stream have little influence on the boundary layers in non-cavitating flow, even for the VGs-Down with vertical distance δ = 0.