Study On The Driving Effect Of Cavitation Bubble Jet On Particles

During the operation of hydraulic machinery,when cavitation and sediment particles exist at the same time,they will have a synergistic effect(i.e."abrasion" effect),which will cause accelerated damage to the flow passage components,and the effect will even exceed the superposition of the separate effects of cavitation or sediment abrasion.Abrasion seriously affects the safe and stable operation of hydraulic machinery,which is one of the key problems to be solved in the field of hydraulic machinery,but its micro mechanism,especially the interaction mechanism between cavitation bubble and sediment particles,needs to be further studied.This study focuses on the jet action generated when the cavitation bubble collapses near the particles,establishes the cavitation bubble jet generation and measurement system acting with the particles,makes a quantitative study on the dynamic characteristics of the cavitation bubble near the particles,the jet strength and its influencing factors,and compares the driving effects of the jet and the cavitation bubble on the particles.The main results of the study are as follows:The particle orifice plate is processed,the cavitation bubble jet generation and observation system is built,the stability and repeatability of experiments such as cavitation bubble generation and jet pressure measurement are tested,and the key experimental parameters are determined.Based on this system,firstly,the evolution process of cavitation bubble under the particle orifice is observed.In the growth stage of cavitation bubble,the centroid position is relatively fixed and basically does not change;In the collapse stage,the centroid of the cavitation bubble begins to move towards the particles,and the moving distance gradually increases with the increase of the cavitation bubble.The basic forms of cavitation bubble collapse are ellipsoid,rod,cone and tooth root.By comparing the experimental results,the growth state,collapse direction,collapse form and jet direction of cavitation bubble and particle are basically the same under the condition of equivalent parameters,which shows the effectiveness of this experimental method.Then,the jet pressure produced by cavitation bubble collapse is measured,and its influencing factors are studied.It is found that the jet pressure decreases with the increase of particle radius;It increases with the increase of the maximum radius of cavitation bubble;It decreases with the increase of the distance between cavitation bubble and particle.The wall velocity of cavitation bubble away from the particle end also reflects the same law as above.At the same time,the Kelvin impulse in the process of cavitation bubble collapse near spherical particles is calculated.Its size and direction can characterize the jet intensity and direction when cavitation bubble collapse near particles.When the cavitation bubble is located at different positions near the particle,the direction of Kelvin impulse always points to the geometric center of the particle.With the increase of the distance between the cavitation bubble and the particle,the absolute value of Kelvin impulse produced by the cavitation bubble near the particle decreases and the jet strength decreases.When the cavitation bubble is generated below the particle,the Kelvin impulse increases with the decrease of the distance from the particle,and the growth rate gradually increases,pointing vertically upward to the particle.Finally,the driving effect of cavitating bubble jet on particles is studied.The jet can accelerate the movement of stationary particles,which can make the particles move away from the cavitation bubble.When the action time is the same,the greater the distance between the cavitation bubble and the particle,the smaller the displacement of the particle and the smaller the maximum velocity;The smaller the maximum radius of cavitation bubble,the smaller the particle displacement and the smaller the maximum velocity;The smaller the particle curvature,the smaller the particle displacement and the smaller the maximum velocity.By comparing the driving effect of jet on particles and the overall effect of cavitation bubble on particles,it is found that the interaction mechanism between cavitation bubble and particles is different in different parameter intervals.The velocity of particles after the action of jet is greater than that after the removal of jet by cavitation bubble,and the jet pressure is greater than the radiation pressure.The jet is the main mechanism of particle movement driven by cavitation bubble,and the particles move away from cavitation bubble at this time;The velocity of the particles after the jet is less than that after the cavitation bubble removes the jet,and the radiation pressure is greater than the jet pressure.The radiation pressure is the main mechanism for the cavitation bubble to drive the particles to move,and the particles move towards it at this time.