Numerical Simulation Of Magnetohydrodynamic Flows In Conducting Pipe

The liquid metal blanket has become an important branch of fusion reactor blanket design because of its simple structure design and easy tritium multiplication and extraction.The flow of metal fluids in the blanket in the fusion magnetic field will produce the magnetohydrodynamic effect,which will affect the redistribution of liquid metal fluids in pipelines,change the flow state of fluids,and have a great impact on the heat and mass transfer of liquid blanket.The factors that affect the MHD effect include Hartmann number,pipe geometry and electrical conductivity,etc.Therefore,it is of great significance to study the relationship and physical mechanism between magnetic fluid flow in circular pipe,and it has important reference value for the design of liquid blanket pipeline in engineering practice.The open source CFD software OpenFOAM is redeveloped by research group.In this paper,The magnetohydrodynamic flow in a conducting pipe is numerically simulated by this solver.Firstly,the magnetohydrodynamic laminar flow of a standard conducting pipe in an external uniform magnetic field is numerically simulated in the range of Re=21375,Ha=85.5?2000 and C=0.0457?0.5.The results show that with the increase of Hartmann number,the thickness of boundary layer will become thinner obviously,and the jet in Robert layer will increase gradually.At Ha=2000,the velocity along the center line of pipe section presents a typical "M" distribution;Wall conductance ratio C can affect dimensionless velocity distribution,including the maximum value of the velocity jet in Robert layer.By changing the conductivity of the pipe wall,the wall of Hartmann layer is conductive while that of Robert layer is insulated.Numerical simulation is carried out in the range of Re=21375 and Ha=85.5?1000,It is found that a very large jet generated in the Robert layer,and the velocity distribution is closer to the conducting rectangular duct.Further,the geometry of the pipe is changed by adding protrusion in the Robert layer on both sides and two protrusion in the Hartmann layer and the Robert layer on both sides,The numerical simulation of magnetic fluid laminar flow is carried out respectively,The results are compared with those of the standard conducting pipe.It is found that the introduction of the protrusion makes the Robert layer produce obvious jet;The velocity distribution,current distribution and MHD pressure drop in F-duct are obviously different from those in N-duct and T-duct.Changing the depth of the protrusion trough into the fluid,it is found that the deeper the protrusion is,the greater jet produced in the Robert layer and the MHD pressure drop will increase.Finally,the large eddy simulation coherent structure model(CSM)and the cyclic boundary conditions are used to simulate the turbulent flow in a conducting pipe with four protrusions and a standard conducting pipe with the same Reynolds number and different Hartmann numbers.Numerical simulation results of two kinds of pipes are compared in terms of turbulent kinetic energy,velocity distribution,pulsation,current distribution,vortex structure distribution and wall friction coefficient.The instantaneous velocity of the N-duct is changed from turbulence to laminar with increasing magnetic field,Adding a protrusion at the center of the boundary layer can effectively stimulate the transverse velocity and form turbulence,which is beneficial to the heat transfer in the liquid blanket,but the friction coefficient of the pipe wall increases slightly.