Numerical Simulation Of Cavitating Flow Of A Finite-span Wing

Cavitation is a very complex vapor-liquid two phase flow includingphase changes and viscous effects. It has been an important phenomenon intechnology and a challenging topic of research in engineering science for thepast100years. Earlier cavitating research based on potential theory andconcerned about the macroscopic hydrodynamic loads. As computationalcapacity improved, numerical simulation of cavitating flow turns to solveReynold Averaged Navier-Stokes (RANS) equation. In the beginning of thiscentury, Large Eddy Simulation (LES) and Detached Eddy Simulation (DES)have emerged recently as a promising approach to simulate cavitating flowscharacterized by high density ratio, large scale flow separation andunsteadiness. Present research intends to explore DES and LES forcavitating flow over a three dimensional finite-span hydrofoil as well asstudying the unsteady hydrodynamic characteristics and evolution of cloudcavitation on a2D hydrofoil.In the present work, the capability of numerical simulation with theReynolds Averaged Navier-Stokes (RANS) equations, Detached EddySimulation (DES) and Large Eddy Simulation (LES) are investigated withshedding and break-off of sheet cavitation and behavior of cloud cavitationover a two dimensional cavitating hydrofoil. Comparing with experimentaldata of a2D hydrofoil, the RANS model with modified turbulence viscosity,DES and LES can reasonably predict the hydrodynamic forces, while DES and LES could accurately predict the frequency of cavity shedding. Thenumerical results of2D LES show that the generation and evolution of thevortex bear the wake of sheet cavity is the primary reason of break-off ofsheet cavitation, and the reentrant jet occurs only after the break of the sheetcavity.For three-dimensional simulations, DES is used to investigate thecharacteristics of the flow field. By comparing the structure of wingtipvortex with the experimental data in single phase flow, DES method isvalidated. The vortex structure, water-vapor interphase and othercharacteristics of the cavitating flow field are obtained through numericialsimulation. Numerical results indicate that the wingtip vortex structure is notaxisymmetric near the trailing edge; the structure becomes axisymmetriconly after developing half chord downstream. Besides, the cavity around thewingtip significantly reduces the vorticity magnitude. DES results also showthe fluctuation characteristics of velocity and pressure in a given free streamflow condition, which can provide basic information of flow field for furtheranalyzing the cavitation induced noise.