Numerical Investigation On Unsteady Cavitating Flows Around A 3D Hydrofoils Based On Aa Non-Linear Mass Transfer Model

Cavitation flow is complex gas-liquid two phase flow,the instability and collapse of cavitation flow could cause the severe impact of hydraulic machinery.It is of great significance to study the cavitation flow mechanism through numerical or experimental methods,and to accurately solve the cavitation flow field and further analyze the cavitation mechanism.In this paper,CFX commercial software is used to simulated the unsteady cavitation of the two-dimensional and Three-dimensional NACA66 hydrofoil by a new mass transfer model and combined DES hybrid turbulence model.The main work as follows:First of all,considering the influence of the non-linear growth of the vacuolar motion(R-P)equation,a new cavitation model for the non-linear growth of the bubble radius is established.The two parameters in the nonlinear cavitation model are combined with the DES turbulence model.The applicability of the initial bubble radius R0 and the non-condensing gas mass fraction fg is explored.The results show that the noncondensable gas mass fraction has important influence on the calculation of cavitation flow.When the non-condensing gas mass fraction fg=1.5×10-6,the predicted airfoil surface cavitation evolution law is consistent with the experiment by comparison.However,the initial cavitation radius R0=1?m which required by the cavitation model is consistent with the prediction results.Second,nonlinear cavitation model and Schnerr-Saure are used to simulate the unsteady cav itation around NACA66 two-dimensional hydrofoil.based on nonlinear model results analyzed and discussed the relationship between hydrofoil surface pressure pulsation and cavitation.The results show that the nonlinear cavitation simulation is better than Schnerr-Sauer model in predicting the average drag coefficient and cavitation volume.The relationship of Pressure the difference pressure pulsation change process of the hydrofoil surface also explains the computation processof sheet cavitation linear growth predicted by the nonlinear model.Then the unstable cavitation flow of the three-dimensional NACA66 hydrofoil is calculated using the nonlinear cavitation model.The evolution process of the three-dimensional hydrofoil surface cloud cavitation were analyzed and research the fundamental cause of the shedding cavitation,based on the results of nonlinear model.The research findings show that the process of cavitation can be clearly observed the whole process of cavitation from two dimensions to three dimensional cloud cavitation and three dimensional transition to two dimensions from the hydrfoil.Re-entrant flow is the cause of the sheet cavitation occurred fracture.Finally,based on the above simulation calculation results,the interaction between cavitation and vorticity is analyzed by combining the vorticity transport equation,and the relationship between cavitation shedding and pressure pulsation is studied through one-dimensional analysis.The results show that the baroclinic torque produced mainly in the vapour interface,in additional cavity internal could be ignored.vortex dilatation term and baroclinic torque cause vorticity alteration.The hydrofoil surface pressure pulsation calculated by the one-dimensional analysis method is basically consistent with the numerical calculation results.