Study On Fluid Behavior In Weld Pool Based On Lattice Boltzmann Method

With the help of numerical simulation,quantitatively analyzing the fluid behavior,especially the process of fluid flow and heat transfer of weld pool,is one of the frontier research topics in the field of welding.At present,most of the simulations about fluid flow and heat transfer of weld pool were mainly based on the continuous medium hypothesis and the Navier-Strodes equation,know as the macroscopic method.This method poses a simple expression and direct vision,and widely used in many numerical simulations,including welding.However,due to base on the continuous medium hypothesis,it is often faced with many difficulties for using macroscopic method to deal with the discontinuous problems,such as the simulation of dendritic growth coupled with natural convection in weld pool.Lattice Boltzmann method(LBM)does not depend on the continuous medium hypothesis,as a fast developing mesoscopic method in recent years,which has been a useful tool for computational fluid dynamics with the advantages of clear physical meaning,convenient implementation,simple boundary treatment and natural parallelism,etc.However,LBM is rarely used in the field of welding numerical simulation,especially for studying on fluid behavior in weld pool.First,based on the basic principle of LBM,and by taking account of the energy and momentum boundary conditions of welding process,as well as the influence of surface tension gradient,buoyancy,and electromagnetic force,a two-dimensional transient model was established to analyze fluid flow and heat transfer of stationary TIG weld pool in this paper.Then,simulated and quantitatively analyzed the fluid behavior with an anode of Q235 low carbon steel.Finally,the verification experiments were done.According to the above research,the results show as follows:(1)Simulated and compared the temperature and flow fields of weld pool due to combine and separate pure conduction,buoyancy,electromagnetic force,and surface tension gradient,which show that the effect of surface tension gradient in weld pool is the most important,electromagnetic force is less important,and buoyancy is the least important.(2)Simulated and compared the temperature and flow fields of weld pool under the same welding current,which show that the convection in weld pool becomes more and more severe,and the width and depth of weld pool has expanded as the time goes on.But the growth of the depth is less than the width.(3)Simulated and compared the temperature and flow fields of weld pool under the different welding current,which show that the temperature gradient,the width and depth of weld pool has developed with the rising of welding current.There is almost no decrease of the growth of the width,however,the growth of the depth become less.(4)The calculations of the model agree well with the experiment,which show our model is reliable.