Study of Large-Eddy Simulation Method for Turbulent-Vortex Cavitating Flow

点击翻译按钮获取中文摘要

We proposed a Large-Eddy Simulation (LES) method for unsteady turbulent flows including cavitation. Particular attention was focused on the modeling of cavitation inception due to the fine-scale turbulent eddies. In addition, the computational scheme for weakly-compressible flows was developed. Major results are as follows:(1) Subgrid scale modeling for LES :We proposed a method to improve the accuracy in the prediction of cavitation inception based on the pressure fluctuation, taking into account the recent knowledge of statistical property of turbulent fine-scale vortices. In addition, high-order finite-difference method for LES with transport equation of subgrid scale kinetic energy in generalized coordinate system for low Mach number flows was constructed.(2) Database by direct numerical simulation (DNS):DNS was applied to a separated turbulent flow in the condition corresponding to an experiment. As a result, we found that fine-scale vortices of Burgers type could cause the cavitation and that the cavitation affects the vortex structure. Then, to model the interaction between turbulent vortices and cavitation phenomena, we applied DNS to a Burgers vortex, which represents the universal property-of vortex in turbulence. DNS database are to be used for the subgrid scale modeling.(3) Algorithmic development :Since the density variation is important in gas-liquid two-phase fluids, we proposed a computational scheme based on the elliptic-type partial-differential equation for pressure, which is suitable for low Mach number flows. Then the efficiency and accuracy were confirmed by applying it to the flow around NACA0012 airfoil and turbulent flow in unstable thermal stratification. In addition, introducing TVD scheme for convective term in the equation of motion, we obtained an improved results for unsteady cavitating flow through two-dimensional cascade.