Numerical simulation on the flow field and slag carrying efficiency of air flush drilling for vertical shaft boring machine

In view of the deficiency of the existing vertical shaft boring machine slag discharge mode,a fluid washing system suitable for a full-section shaft driving is proposed by referring to the fluid washing and slag discharge mode of large diameter shaft drilling rig. Based on some assumptions and combined with actual working conditions,the basic parameters and typical parameters of fluid well washing system are determined. FLUENT fluid simulation software is mainly used to carry out the numerical simulation of air well washing flow field and slag removal efficiency. First,the basic parameters of the air well cleaning system are optimized through single-factor numerical analysis,and the radial tangential and vertical velocity components and the eddy current in the bottom hole are used as the evaluation indexes to obtain a set of optimal well flushing system parameters to a certain extent. Through orthogonal test analysis,the influence law of parameters such as the inner diameter of slag discharge pipe and the angle of jet nozzle on the flow field at the bottom of the well is obtained. The inner diameter of the slag discharge pipe has the greatest influence on the flow field at the bottom of the well,while the angle of the jet nozzle and the included angle between the cutter head and the bottom of the well have the least influence. Second,the numerical simulation of gas-solid two-phase flow is carried out. The cuttings are assumed to be homogeneous spherical particles and set as discrete phase,the cumulative cuttings discharge quality and mass rate of cuttings discharge as well as slag removal rate and slag carrying rate are used as evaluation indexes,the influence law of inlet air flow at cuttings particle size and slag discharge height on the effect of well washing and slag discharge are obtained. There is a negative correlation between the effect of well flushing and debris particle size and a positive correlation between the air flow at the entrance,and the height of discharge has little effect on the effect of discharge. Finally,the verification of the similarity model test is briefly introduced,based on the similarity criterion derived,the similarity modeling design is carried out. The model experiment with a geometric similarity ratio of 1:20 is completed by using a self-designed and processed model experiment table. The law obtained by model experiment and numerical simulation is basically the same,which indicates that the numerical calculation results have certain accuracy,and provides a theoretical basis and basic parameters for the follow-up largescale model experiment or field experiment.