Large Eddy Simulation Of Geometry Sensitivity Of Magneotohydrodynamic Turbulent Rectangular Duct Flow

The study of magneotohydrodynamic turbulence is of great significance for the design of liquid metal blanket in nuclear fusion reactors.Large eddy simulation is widely used in magneotohydrodynamic turbulence due to its low requirement of mesh precision,high calculating speed and accuracy.The geometrical effect of the cross-section of the duct is an important factor in liquid metal blanket conceptual design to reduce the magneotohydrodynamic pressure drop and promote the heat transfer.Firstly,based on the open-source CFD software OpenFOAM,Coherent structure model is developed and embedded in the MHD solver,and the turbulent flow in a square duct is numerically simulated.the numerical simulation results of the same parameters with the Coherent structure model in OpenFOAM are compared with the kabayashi results to the accuracy of the model in OpenFOAM environment,which shows that it can be used in the numerical simulation of Magneotohydrodynamic turbulent.After that,the validated Coherent Structure model is applied to the numerical simulation of turbulent flow in two different geometries duct,One duct has a normal rectangular crosssection(N-duct),while the other rectangular duct has a triangular protrusion pointing into the flow domain at the middle of the walls parallel to the magnetic fields(P-duct).While both duct walls are electrically insulating,and the inlet and outlet of the computational domain are set to be periodic,the flow Reynolds number is kept constant,the Hartmann numbers vary from 10 to 42.4.The numerical results showing,because of the influence of secondary flow near the protrusion,As the Hartmann number increases,the turbulent MHD flow transits to a single-sided turbulent flow and finally to laminar flow,The single-sided pattern is a critical pattern which indicate the transition of ‘turbulent-laminar',The transition is determined by the ratio of Reynolds number to Hartmann number(Re/Ha),which is 214.38 for N-duct,while it equals 183.26 for P-duct.The protrusion at the parallel walls promotes flow turbulence and increase turbulent kinetic energy,this has a good effect on the heat transfer in the liquid metal blanket.However,the skin friction coefficient of the wall is increased.Finally,the numerical simulation of the flow in the wall conductive duct with protrusion is carried out.It is found that when the magnetic fluid in the conductive duct is in a laminar flow state,a jet will be generated near the parallel layers on both sides of the duct and the jet will increase with the increase of Hartmannian number,While this jet stream does not occur in turbulence flow.In summary,the protrusion of duct is conducive to promote turbulent and promotion of heat transfer,but it can increase the skin friction coefficient of the wall.The geometrical effect of the cross-section of the duct is an important factor in liquid metal blanket conceptual design.