Numerical Simulation Of Magnetohydrodynamic Flows In A Pipe

Liquid metal in the thermonuclear fusion liquid blanket flows under strong magnetic field.Liquid metal is influenced by the strong magnetic field to produce the induced current.The induced current interacts with the magnetic field to generate Lorentz force,which causes the effect of Magnetohydrodynamics(MHD).The MHD effect changes the flow state of the liquid metal,and affects the heat transfer of the blanket and the efficiency of the transport of the material in the blanket.The MHD effect is related to Reynolds number,Hartmann number,wall electrical conductivity and geometrical shape.Therefore,to clarify the physical mechanism of MHD effect and its influence have a important guiding for the design of blanket in Engineering.In this paper,the large eddy simulation method CSM model is adopted,and the Map turbulent boundary condition is used to simulate the turbulent flow under the uniform magnetic field in the insulated circular pipe.According to the simulation results,the distribution characteristics of the velocity and current in the pipe are analyzed.The suppression of the fluctuating velocity of the turbulence by magnetic field is anisotropic.The wall friction coefficient is agreement with the Zikanov's simulation and the Hartmann's experiment result.The results show that the proposed grid,boundary conditions,LES and CSM models are feasible,which provides a reference for the subsequent numerical simulation of the turbulent magnetic fluid in the circular pipe.Further,numerical simulation of laminar flow of magnetic fluid in a conducting circular pipe under uniform magnetic field is studied.The simulation results show that,on the condition of the same Reynolds number and wall conductivity,the greater Hartmann number,the velocity boundary layer becomes thinner;core velocity inhibited by magnetic field is stronger,the speed becomes smaller,and the core area of fluid flows from Robert layer to the wall.Due to the smooth geometry of the circular pipe and small Hartmann number(Ha=160?320),the "M" velocity jet in the Robert layer is not obvious.While the Hartmann number become large(Ha=1217),the "M" velocity jet begins to appear.At the same time,the larger Hartmann number,the greater MHD pressure drop.The laminar flow is simulated under non-uniform magnetic field in a conducting circular pipe and compared with the results of the ALEX experiment.The simulation results are in good agreement with the experimental results.The results show that,the fluid-solid coupling solver developed by the research team under low magnetic Reynolds number has high accuracy and reliability,which can be applied to the numerical simulation of MHD pipe flow under non-uniform magnetic field.Finally,the large eddy simulation of MHD turbulence flow in a conducting circular pipe under non-uniform magnetic field is studied.The simulation results show that,the velocity jet instability first appears in the Robert layer,and then,with the weakening of the magnetic field strength,the stronger turbulence is gradually generated along downstream.The peak values of the streamwise pressure difference and the transverse pressure difference increase with the increase of Hartmann number.The variation of the magnetic field leads to the three-dimensional effect of the current in the direction of the flow,and the vortex structure in the pipe also changes gradually.In the rising and falling phases of the magnetic field,a special wavy vortex structure appears near the wall.