Research On Dust-raising Mechanism Of Blast Shock Wave In Tunnel

For a long time,fossil energy has always occupied a dominant position in my country’s energy supply,among which coal resources account for the highest proportion.Moreover,coal,as an important strategic material in my country,will still play a very important role in the country’s infrastructure construction in the future.During the mining process of underground coal mines,a large amount of deposited coal dust will be generated.When blasting operations or an explosion accident occurs,the shock wave generated by the explosion will lift up the deposited coal dust to form a coal dust cloud,and the coal dust cloud will be ignited when encountering an open flame.Secondary coal dust explosion accidents are prone to occur.At present,there have been many conclusions in the research on the mechanism of sedimentary coal dust hoisting,but there are also some problems,mainly as follows: the lack of systematic theoretical analysis on the force of coal dust particles;the cause of sedimentary coal dust raising is not yet very clear;the analysis of the hoisting process of coal dust particles is not clear enough.In view of the above problems,this paper mainly studies the hoisting mechanism and hoisting process of deposited coal dust under the induction of explosion shock wave.The main research contents are as follows:First,all the forces that individual coal dust particles experience in the fluid are investigated.Secondly,using order of magnitude analysis,the main forces that can affect the lifting process and movement trajectory of coal dust particles under the high-speed and high-pressure blast shock wave flow field are studied.The results show that coal dust particles are mainly affected by gravity,Saffman force,aerodynamic drag,pressure gradient force,particle collision force and turbulent diffusion of particle phase.Then,using the methods of theoretical analysis and numerical simulation,the propagation law of the blast shock wave in the confined long straight roadway is studied.The results show that during the propagation process of the explosion shock wave,the air flow in front of it will be pushed and compressed to form a disturbed air flow in front of the wave;with the propagation of the shock wave,the pressure and velocity of the shock wave front,the disturbed airflow in front of the wave and the high-speed airflow behind the wave show a decreasing trend.The propagation speed of the explosion shock wave is inversely proportional to the square root of the propagation distance,the overpressure is inversely proportional to the propagation distance,the high-speed airflow behind the wave is inversely proportional to the square root of the propagation distance,and the propagation distance of the shock wave is proportional to the square root of the propagation time.Finally,by means of numerical simulation and experimental verification,the mechanism of depositional coal dust raising induced by explosion shock wave is studied.The results show that the lifting process of the deposited coal dust is caused by the combined action of the explosion shock wave front,the disturbed airflow before the wave and the high-speed airflow behind the wave.The disturbed airflow can change the initial accumulation state of the coal dust particles.The lifting of coal dust particles has mainly gone through four stages: start-up stage(acceleration rising stage),deceleration rising stage,sedimentation stage and pneumatic transport stage.In the start-up stage,the coal dust particles are mainly affected by the Saffman force and turbulent diffusion,and rise rapidly;in the deceleration and uplift stage and the settling stage,the coal dust particles are mainly affected by gravity and aerodynamic resistance,and the coal dust particles first decelerate and rise to the maximum height and then start to settle;In the pneumatic transport stage,most of the coal dust particles return to the boundary layer,and their movement in the vertical direction tends to be stable,mainly as they move towards the tunnel exit under the action of aerodynamic resistance.The coal dust particle group has a tumbling motion in the acceleration up stage and the subsidence stage respectively,and the particle group moves forward in the form of "rolling".To sum up,this paper mainly studies the whole cyclic movement process of sedimentary coal dust from "static-rising-settling" under the induction of explosion shock wave,which provides a certain reference for the formulation of explosion-proof and explosion-suppression measures in underground coal mines.