The Effect Of Surfactant Drag-Reducing Additives On The Characteristics Of Cavitating Flow Around A Hydrofoil

Hydrofoil cloud cavitation has strong unsteady characteristics,and it is easy to produce vibration,noise and cavitation erosion,and at the same time,it will increase the navigation resistance.Some scholars have proposed that the method of reducing the surface tension of liquid can be used to promote the cavitation flow around hydrofoil to reach supercavitating state quickly,so as to reduce the drag of hydrofoil during navigation.At the same time,surfactant solution also has the effect of turbulent drag reduction.Therefore,the effect of surfactant solution on cavitation flow around hydrofoil is studied in this paper.Firstly,the numerical simulation of cavitating flow around a two-dimensional hydrofoil is carried out.The effect of surfactant solution on cavitating flow around hydrofoil under different attack angles and cavitation numbers is investigated,and the influence of surfactant solution injected through slit on cavitation flow around hydrofoil cloud is analyzed.It is found that the cavity shedding in the surfactant solution is faster than that in the water,and the cavitation shedding period around the hydrofoil cloud is the smallest when the surfactant solution is injected through the slit.This shows that the development of cloud cavitation can be promoted by changing the physical properties of local fluid.Secondly,the numerical simulation of cavitating flow around a three-dimensional hydrofoil is carried out.In the cavitating flow around a three-dimensional hydrofoil,the evolution laws of cavitating cavitation around hydrofoil in water,surfactant solution and injection through slit are compared and analyzed.It is found that the cavitation evolution process of cavitating flow around hydrofoil is similar in three cases,but the shape of cavitation is different in each stage.Generally speaking,the evolution of cavitation in surfactant solution is more advanced and faster than that in water.The drag characteristics of the three cases are analyzed and compared.The results show that both the surfactant solution and the surfactant solution injected through the slot can slightly reduce the drag of the hydrofoil,which is due to the turbulent drag reduction effect of the surfactant solution itself.Finally,the vortex structure and the interaction between cavitation and vortex structure are analyzed.The Q-method is used to analyze and compare the vortex structure characteristics of cavitation around hydrofoil in water,cavitation around hydrofoil in surfactant solution and cavitation around hydrofoil injected with surfactant drag reducer solution.It is found that surfactant solution can restrain small-scale vortices.At the same time,the vorticity distribution of the three cases was compared by using the vorticity transport equation.It was found that the extent of the vortex stretching term and the vortex expansion term was the highest in the cloud bubble shedding area,and the cavitation breaking was the most obvious in the three cases.This is because the surfactant reduces the surface tension of water,promotes boiling and enhances heat transfer.Under the same conditions,the number of vaporization cores in water increases obviously,which is conducive to the growth of bubbles and has a positive effect on the collapse of bubbles.