| Aiming at the problems of high environmental resistance and low rock breaking efficiency in the process of underwater rock breaking,a new method of gas-assisted water jet rock breaking is proposed.Based on the theory of water jet impact dynamics,cavitation dynamics and fluid-solid coupling theory,combined with numerical simulation and scientific experiment,the flow characteristics,rock breaking mechanism and rock breaking lithology of underwater gas-assisted water jet are analyzed.The influence of gas pressure and nozzle structure parameters on the axial velocity development and flow pattern of underwater gas-assisted water jet is obtained,the rock breaking mechanism under the impact of underwater gas-assisted water jet is revealed,and the influence of different nozzle structure parameters and jet working parameters on the rock breaking performance is explored.This study provides a scientific basis for improving the efficiency of underwater rock breaking by water jet.Based on the gas-liquid two-phase flow theory,the basic structure of the underwater gas-assisted water jet is described.The characteristics of different regions and their influence on rock erosion are analyzed,and the flow characteristics of downward gas jets in water are studied.On this basis,the underwater gas penetration depth equation is established.Furthermore,the fluid structure interaction model of cavitating micro jet impinging on the wall is established by combining the cavitating dynamics and the velocity equation of cavitating micro jet.Finally,the homogeneous flow model is used to study the impulsive dynamic pressure mathematical model of the gas-liquid mixed-phase jet,and the mathematical expression of the impulsive dynamic pressure of the gas-liquid mixed-phase jet is obtained.Based on the Mixture multiphase flow model and the LES turbulence model,the numerical models of flow fields of the underwater gas-assisted water jet nozzle are established.Research on the inner and outer flow fields of the nozzle of the underwater gas-assisted water jet is carried out.The results show that compared with the pure water jet,the presence of the auxiliary gas in the underwater gas-assisted water jet reduces the resistance of the environmental water to the water jet and delays the attenuation of the water jet’s flow energy.After the water jet enters the external environment,as the airflow pressure increases,its axial velocity shows a trend of first increasing and then decreasing.As the system pressure increases,the attenuation of the axial velocity of the water jet is more gentle.The axial velocity of the water jet under the constricted section of different outer nozzles is as follows: exponential type>cone type>circular type>cylindrical type.The axial velocity of the water jet increases first and then decreases with the increase of the diameter of the outer nozzle outlet and the length of the straight section.The research results can provide a basis for the design of gas-assisted water jet nozzles.In order to reveal the rock breaking mechanism of the underwater gas-assisted water jet,the influence of different air pressure,the structure of the contraction section of the outer nozzle,the outlet diameter and the length of the straight section on the flow pattern of the underwater gas-assisted water jet was analyzed,and related experimental studies were carried out.In order to explore the rock-breaking performance of the underwater gas-assisted water jet during the erosion at a fixed point,a corresponding rock-breaking test system was built,and the influence of gas flow pressure,nozzle structure parameters and erosion time on the rock-breaking performance was studied through experiments.The research results further explain the rock breaking mechanism of the underwater gas-assisted water jet,which can provide guidance for related rock breaking performance research.In order to analyze the influence of system pressure,erosion distance,incident angle and lateral movement speed in the process of underwater gas-assisted water jet rock breaking on rock breaking volume,breaking depth and rock breaking specific energy consumption,and to obtain the best combination of working parameters for underwater gas-assisted water jet rock breaking,researches on single factor and orthogonal experiments were carried out respectively.The experimental results show that the system pressure has the greatest influence on the rock breaking performance,the incident angle is the second,the lateral speed is the second,and the erosion distance is the least important.The system pressure should be selected as high as possible.The best values of other working parameters are as follows: traverse speed of 3 m/min,incident angle of 75°,and erosion distance of 10 mm.There are 54 pictures,15 tables,and 138 references in the thesis. |
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