Study On The Acceleration Dynamics Of Abrasive In Premixed Abrasive Water Jet

The premixed abrasive water jet is widely used in field ofoil and gas exploitation.The accelerating efficiency of the fluid on the particle is the key factor affecting the cutting performance of the premixed abrasive water jet.At present,the research on the premixed abrasive water jet is not enough,and it is lack of the intensive research on the mechanism of the abrasive acceleration in the external flow of the nozzle.In the numerical simulation,the abrasive is treated as pseudo-fluid,it is considered that the abrasive is in the form of continuous phase which coexists in the premixed abrasive water jet with wataer.Due to the high velocity of abrasive jet,the abrasive velocity can not be measured directly to verify the existing particle velocity model.Therefore,it is significant to study the acceleration dynamics of abrasive in premixed abrasive water jet in order to improve the efficiency of the premixed abrasive jet,optimize the structure of the nozzle,and determine the optimal target distance of the premixed abrasive water jet.In this paper,based on the two-phase fluid dynamics theory,the acceleration mechanism of abrasive in the premixed abrasive water jet is studied.By using the computational fluid dynamics discrete element method,the motion of the abrasive in the premixed abrasive water jet is simulated.PIV technology is applied to test the abrasive velocity in abreasive water jet,whihc is used to verify the theoretical model and numerical simulation.The main results are as follows:(1)A new method of abrasive jet velocity measurement based on PIV is proposed.This method uses the PIV system to obtain the original image of abrasive jet.The position information and the velocity of the abrasive in the abrasive water jet can be quickly obtained combined with the self programming program.This method provides an experimental basis for the study of the acceleration dynamics of abrasive in the premixed abrasive water jet.(2)The dynamics models of abrasive acceleration in the high pressure pipeline,nozzle and external flow field of nozzle were established.The model is solved by a numerical method based on bisection method and iterative algorithm,and the results are verified by PIV test.When the abrasive moves in the high-pressure pipeline,the abrasive velocity increases with the increase of the moving distance,The velocity of the abrasive entering the nozzle is approximately equal to the water velocity of the high pressure pipe.When enter a nozzle with a limited length,abrasive has been in the accel-eration process,the abrasive velocity will gradually increase,but still less than water velocity.The abrasives flow in the external flow field of the nozzle exists a flow expansion.The diffusion angle of abrasives is smaller than that of pure water jet.The abrasives ejected from the different radial positions of the nozzle exit experience a process of acceleration and deceleration.The difference is that they have different acceleration distance.Part of the abrasives are not only accelerated in the initial segment,but also accelerate in the basic segment.The average percentage error and standard deviation between the measured values and the theoretical values are less than 4% and 5m/s respectively.The measured values are in good agreement with the theoretical values.The correctness and accuracy of the theoretical model are verified.(3)Based on the single phase coupled field data loading method,the abrasive is modeled by discrete element model and the water is modeled by the continuous medium model,the movement of the abrasives in the high pressure pipeline,the nozzle and in the external flow field of the nozzle were simulated by using FLUENT and EDEM software.And the results are verified by PIV test.The results show that The velocity and the trajectory of abrasives were obtained.The average percentage error and standard deviation between the measured values and the theoretical values are less than 3% and 1.5m/s respectively.The measured values are in good agreement with the simulation values.The correctness and accuracy of the simulation results are verified.The research results of this paper contribute to the improvement of the acceleration mechanism of the premixed abrasive jet,which will help to development the technology in all walks of life.