Numerical Study On Nuclei Evolution And Cloud Cavitation Around Hydrofoil Flow

Cavitation is a common phenomenon in the field of ship and ocean engineering.For example,cavitation may occur in the tail flow field of high-speed rotating propeller and the surface of high-speed underwater vehicle.The existence of nuclei is a necessary condition for cavitation,and the formation of cavitation is the process of cross-scale nuclei’s growth.Tracing the nuclei in the flow field is helpful to understand the mechanism of cavitation.The re-entrant jet,pressure wave generated by bubble collapse radiation and vortex flow in flow field are the most important factors that lead to the instability of cavitation,and further affect the development of cavitation.Based on OpenFOAM platform,an Euler-Lagrange nuclei calculation model and a cavitation calculation model considering compressibility of flow field are developed,the cavitation generation and development process in hydrofoil flow field are numerically studied,and conclusions about the evolution law of nuclei,the development law of cavitation flow and the force on hydrofoil surface during the development process are obtained,which provides a reference to the high precision simulation of cavitation flow,the design of underwater vehicle and the study of cavitation erosion.The main research contents of this paper are as follows:Firstly,the Euler-Lagrange nuclei calculation model and the 2D and 3D hydrofoil cloud cavitation numerical models taking into account the compressibility of the flow field are established,and the effectiveness of the numerical models established in this paper for hydrofoil flow field simulation is verified.The lifting resistance and cavitation evolution law calculated in this paper are in good comparison with the published literature.Secondly,based on the Euler-Lagrange nuclei calculation model,the evolution of nuclei in the vortex flow region and hydrofoil flow field during cavitation generation is studied.The cavitation time of the nuclei in the Rankine vortex is related to the location of the initial injected nuclei and the size of the initial injected nuclei.As the location of the initial injected nuclei becomes farther from the vortex center,the cavitation time of the gas core increases exponentially.LES turbulence models are used to study the evolution characteristics of the nuclei in the hydrofoil flow field.It is found that the vortex flow will involve the nuclei in the flow field near the hydrofoil surface,creating conditions for the development of cavitation near the hydrofoil surface.Next,the evolution of cavitation cloud in hydrofoil flow field is studied by using cavitation calculation model which takes into account compressibility of flow field.It is found that the cavitation fracture attached to the hydrofoil happens from the tail of the hydrofoil,and starts to fall off layer by layer on the side cavitation is contacted with the incoming flow until the attachment cavity has completely falled off.The cavitation falling off the tail of the threedimensional hydrofoil presents an inverted U shape.In a single cycle,the farther the position of the hydrofoil suction surface is,the longer the period of high pressure action will be.Finally,the influences of Reynolds number,cavitation number and Angle of attack on hydrofoil cavitation flow evolution are studied based on the research of hydrofoil cloud cavitation evolution.With the increase of Reynolds number,the vortex flow in the cavitation region gradually strengthens,the length of the cavitation region gradually increases with the decrease of the cavitation number,and the thickness of the cavitation region gradually increases with the increase of the Angle of attack.