CFD Simulation Of The Relationship Between Liquid Jet And Aeration Cavitation In A Vehicle

In the past two decades,supercavitation has been widely used in drag reduction of vehicles.After supercavitation was formed on the surface of the vehicle,the friction resistance will decrease significantly,so as to greatly improve the navigation speed.Due to the instability of natural cavitation and the harsh conditions of formation,the supercavitation drag reduction is usually achieved by artificial ventilation.In the case of artificial ventilation,the air source of supercavitating vehicle is limited and it is difficult to realize long-time ventilation.When the navigation depth is too high,the water pressure will lead to the contraction of gas volume,which is difficult to achieve the ideal drag reduction effect.Therefore,how to change the pressure distribution on the surface of the vehicle,weaken the phenomenon of gas volume contraction and maintain the supercavitation shape with small ventilation mass flow has become a problem to be solved in the design of supercavitating vehicle.In view of the above problems,this paper considered the possibility of using liquid jet to reduce the pressure distribution on the surface of the vehicle.2-D flat plate and supercavitating vehicle are studied by numerical simulation.The main contents are as follows:This paper derived and summarized the theoretical and empirical formulas for calculating diameter,length and shape of supercavitation and navigation resistance supercavitating vehicle,designed a reasonable shape of the vehicle and supercavitation,calculated the operating parameters according to the designed supercavitation shape,analyzed the grid irregularity,and demonstrated the accuracy of the numerical simulation methods used in this study.Based on SST k-ω turbulence model and VOF multi-phase flow model,the cavitating phenomena of 2-D flat plate surface were studied by referring to existing experiments and numerical simulation at home and abroad.The variation laws of cavitation size,cavitation evolution velocity,cavitation stability and the distribution of shear stress on the surface of the2-D flat plate surface under different jet directions,jet velocities and jet depths were discussed,and the shape of artificial ventilation cavitation close to that of the water tunnel experiment were obtained by simulation.According to the conclusions of 2-D flat plate simulation,the suitable liquid jet scheme was selected,and the cavitating phenomenon on the surface of supercavitating vehicle was simulated.This paper studied the effects of liquid jet on the morphology of natural supercavitation at low speed and artificial ventilation supercavitation at low ventilation mass flow and compared the radius and length of cavitation and the distribution of shear stress on the surface of vehicle before and after adding liquid jet.The results show that liquid jet can promote natural cavitation and artificial ventilation cavitation.After supercavitation was realized by liquid jet,the resistance coefficient decreases significantly.Through numerical simulation,this paper analyzed the influence mechanism of liquid jet on supercavitation shape and the drag reduction effect on 2-D flat plate and vehicle,which has a certain reference significance for the design of supercavitating vehicle.