| Cavitation is a dynamic phase-change phenomenon that often occurs in the flow over rudders,propellers,pumps and other fluid machinery.It is recognized that cavitation occurs when the local pressure drops below the saturated vapor pressure,and collapses in the area where the pressure recovers to large enough,which may lead to several problems such as loss of hydrodynamic performance,vibration,erosion and noise on the surface of fluid machinery.Therefore,accurate simulation of cavitation flow becomes more and more significant in the section of propeller design.The early research objects of cavitation problem are some rotating bodies or hydrofoils with simple geometry,such as cylinder cavitation flow,two-dimensional hydrofoil cavitation flow and so on.A large number of scholars have done comprehensive experimental research on these models,and they provided abundant experimental data.Their contributions have become standard examples for other researchers to carry out research on cavitation.The research on propeller cavitation started in 1990 s and developed a lot during the last two decades.Because of the complexity of its physical problems,it is common to use experimental methods,relying on the experience and data of model test to study the cavitation performance.This method is very intuitive.But it has scale effect and costs lots of money.Therefore,the numerical simulation method of propeller cavitation has become more and more popular.Firstly,the governing equations for numerical simulation of cavitation flow are given in this paper.Cavitation flow is a two-phase flow problem with phase transition.The governing equations include four parts: continuity equation,momentum equation,phase equation and mass transfer equation.These equations are deduced in detail in the text.Then the mass transfer equation,i.e.cavitation model,is described in detail.The popular cavitation models based on transport equation,such as Singhal model and SchnerrSauer model,are introduced and deduced.Then the turbulence models used in this paper are introduced including the viscous modified SST k-omega model.The reliability of the solver is verified by simulating the steady cavitation flow around cylinder.Then,the unsteady cavitation of two-dimensional hydrofoil is forecasted.The phenomena of cavitation growth and shedding are simulated,and the regular periodic variation of unsteady cavitation is summarized.Finally,the reliability of viscous modified SST k-omega model is validated according to the shape of cavitation and shedding frequency.After that,the model is used in the cases simulating the cavitation flow around three-dimensional hydrofoil.Satisfactory results are also obtained in the simulation of three-dimensional hydrofoil TWIST-11 N,and typical cavitation patterns such as horseshoe cavitation are successfully simulated.Through the analysis of velocity vector diagram of hydrofoil cavitation flow fields,it is found that re-entrant jet is the main cause of cavitation shedding in the cases of two-dimensional hydrofoil NACA0015.For three-dimensional twisted hydrofoil TWIST-11 N,it can be found that there are two types of shedding in the 3D cavitation flows which is different from the cases in the 2D cavitation flows.These two types of shedding are known as primary shedding and secondary shedding.They are caused by the re-entrant jet and the side-entrant jet respectively.For propeller cavitation flow simulation,the cavitation solver based on dynamic grids is used,called interPhaseChangeFOAM,and a standard model propeller PPTC is used in the study.The cavitation flow fields under three different conditions provided by the experiment was predicted.The hydrodynamic performance parameters of the propeller with cavitation and no-cavitation were compared.It was proved that the cavitation would cause the loss of propeller's thrust performance.According to the pressure map of the blades,the reason for the loss of thrust was that the cavitation restrained the growth of the zone with low pressure. |
PDF Full Text Request