Study On The Influence Of Concave And Convex Wall Parameters On The Dynamic Characteristics Of Single Cavitation Collapse

Cavitation and cavitation erosion are ubiquitous phenomena.In practice,cavitation mostly occurs on irregular surfaces.Cavitation on the material surface will form pits of different sizes.The newly formed surface affects the surrounding flow field.At the same time,the synergistic effect of spherical particles and cavitation in the water flow may aggravate cavitation and wear.Studying the cavitation dynamics near these walls is of great significance for the suppression and utilization of cavitation.Cavitation contents are divided into condensed gas(water vapor)and noncondensed gas.In this paper,the properties of cavitation contents are considered.For non-condensed gas,the oscillation characteristics of cavitation are solved theoretically based on Rayleigh-Plesset equation.The cavitation dynamics of condensed gas is studied by numerical simulation.Cavitation collapse near pits and hemispherical walls is studied by using numerical simulation The morphological evolution of cavitation near different wall surfaces and the propagation characteristics of pressure wave are discussed.The influence of different wall curvature on cavitation collapse time,jet velocity and wall impact load are discussed in detail.The flow field characteristics and the distribution of shear rate on the wall surface are discussed in detail Specific research conclusions are as follows:1.Based on the solution of the near-wall cavitation translation equation,it is shown that the sub-Bjerknes force decreases with the decrease of the cavitation translation velocity of the dimensionless wall distance γ The larger the wall curvature is,the smaller the distance of cavitation to the wall is,and the maximum value of cavitation translation velocity decreases with the increase of wall curvature ξ.2.Numerical simulation of non-spherical collapse of cavitation near different wall surface shows that the concave wall surface has a stronger effect on the collapse of cavitation than the flat wall surface.The shape of cavitation at the end of collapse determines the jet velocity When the curvature ξ of concave wall increases,the cavitation collapse time prolongs,and the jet velocity decreases.When γ=1.0,the maximum pressure at the center of the concave wall first increases and then decreases with the increase of wall curvature When γ=1.5,the maximum impact load on the center of concave wall increases with the increase of wall curvature The region of high shear rate on the concave wall is always distributed at the exit of both sides of the concave,and the minimum value of shear rate on the hemispherical wall appears near the exit of the wall When the curvature of the concave wall increases,the peak value of the shear rate increases rapidly.3.At the same dimensionless distance γ,the velocity of cavitation jet near the hemispherical wall is higher than that of the concave wall When γ=0.8,the peak pressure at the center of the hemispherical wall increases firstly and then decreases with the curvature of the wall.Under the condition of γ=1.7,The pressure peak value at the center of the hemispherical wall increases first and then decreases with the curvature of the wall,but the inflection point moves backward Under similar conditions,the pressure of cavitation collapse on the hemispherical wall is higher than that on the concave wall.4.When γ=0.8,the peak value of shear rate increases first and then decreases with the curvature of hemispherical wall,and gradually approaches the center of wall.With the increase of curvature of hemispherical wall,the peak value of shear rate is far away from the center of the wall and then close to the center of the wall when γ=1.7,but the peak value of shear rate is far away from the center of the wall.