| Radial drilling technology is mainly used to mine coalbed methane.The performance of its key component—the self-propelled rock-breaking bit directly affects the efficiency of rock-breaking drilling.The combination of direct jet and rotary jet not only solves the problem of the central boss in the rotary jet punching hole,but also retains the diffusivity of the flow field and improves the self-advancing speed of the drill bit.However,the internal structure of the direct rotary mixed jet drill bit has not been optimized.Further research is needed to maximize the drilling efficiency of the drill bit.This paper first theoretically analyzes the structure of the flow field of the straight jet,the rotating jet and the straight swirling mixed jet.Combining the punching characteristics of the three jets,the flow field characteristics and the rock breaking mechanism of the straight swirling mixed jet are obtained.The internal and external flow fields of the mixed jet drill bit are analyzed for the velocity field,and the selection of drill bit structure parameters is obtained.Finally,through the drill bit punching experiment and analysis of the hole shape characteristics,the optimized structure parameters of the drill bit are compared.The main research results obtained are as follows:1)In theory,first analyze the flow fields of the direct jet and the rotating jet,and obtain two jet flow field structures,and discuss their rock-breaking characteristics.It is concluded that the direct jet and the rotating jet are in the form of rock breaking Different,the direct jet energy is concentrated,the main rock breaking form is the water hammer pressure of the droplets,while the rotating jet rock breaking form is mainly the shearing failure of the jet,its rock breaking efficiency is greater than the direct jet rock breaking,and the direct rotating mixed jet effectively combines The flow field characteristics of the straight jet and the rotating jet,combined with the flow field distribution of the combined jet,divide the flow field of the straight mixed jet along the axial direction:the initial section,the basic section,the transition section and the uniform mixing section,and the division along the radius:direct injection Flow zone,strong swirl jet zone,weak swirl jet zone and peripheral jet,while the jet impact damage to the rock is divided into three stages:the initial rock failure stage,the punching micro-pore stage and the macro-fragmentation stage.2)Use Creo software to establish the internal and external flow field model of the straight-rotating mixed jet bit,use FLUENT simulation software to simulate the inner and outer flow fields of the straight-rotating mixed jet,and post-processing the simulation results to obtain the velocity of each cross section of the bit inside and outside the flow field According to the analysis and comparison,it can be concluded that the direct-rotating mixed jet mainly comes from the impeller inside the drill bit.The central hole of the impeller produces a direct jet,and the impeller groove produces a rotating jet.Narrow action,until the flow field of the front nozzle is fully mixed and the speed reaches the maximum value,by adjusting the flow field diameter of the center direct jet and analyzing the external flow field,it can be obtained:as the proportion of the direct jet increases,the center velocity of the direct swirling mixed jet increases,The diffusion angle is gradually reduced,so a good balance of the ratio of the direct jet and the rotating jet is the key to affecting the performance of the jet flow field.Based on the analysis of the simulation results of the direct-rotation mixed jet flow field,combined with the research of the previous scholars,the selection of the direct-rotation mixed jet drill bit is designed:the diameter of the center hole is 0mm,0.8mm,1.2mm and 1.6mm,and the impeller groove inclination angle is 35°,40°,45° and 50°,the width of the impeller groove is 0.5mm,0.7mm and 0.9mm,and the radial length of the impeller groove is 2.5mm,3mm,3.5mm and 4mm.3)According to the drill bit structure selection obtained by the simulation,drill bits with different parameters are processed,and the erosion experiment is performed on the drill bit with different parameters.The test object is a cement specimen.Based on the field expansion angle,the optimal structural parameters of the drill are obtained by comparative analysis:the impeller groove inclination angle is 40°,the center hole diameter is 1.2mm,the impeller groove width is 0.7mm,and the radial length of the impeller groove is 3mm.The research results of this thesis provide a certain theoretical guidance for water jet radial drilling technology,which enriches the research on flow field characteristics and rock breaking mechanism,etc.,and has certain significance.Figure[59]Table[8]Reference[91]... |
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