Numerical Simulation Of Flow Field In Mental Melt By Shear Agitation

Semi-solid metal forming is a hot research point of the metal processing technology inrecent years, and shear flow plays an important role in the formation of spherical crystals insemi-solid slurry, but the current investigation is limited to the comparison betweenexperimental parameters and experimental results, and the intrinsic relationship between theflow field and semi-solid microstructure is not explain in nature. In this thesis, the state offlow field of metal melt by shear aditation is investigated by the FLUENT software, which isbased on computational fluid dynamics theory and the semi-solid organization formationmechanism in current. The flow field of the melt under stirring is simulated by buildingdifferent model, meshing, determining the boundary conditions of the flow field, and theeffect of the stirring speed and surface roughness on the flow field is studied.This is the first time to description the flow field distribution during the shear stirring ofmetal melt, and the motion of the flow field have much difference in different geometric andmotion parameters. When the rotational speed is small, speed, vorticity and velocity vector isuniform stratification, values near the rotor is relatively large; with increasing rotational speed,velocity, velocity vector and vorticity occurs the local instability state; when rotational speedincrease to a certain extent, the whole fluid region is in the state of the development oflaminar flow to the turbulent flow, and the distribution is in periodic axially, and the vorticitydistribution in a number of annular regions in the entire axial near the rotor; When therotational speed reaches2388r/min, the state of vortex appeared on the velocity vector map,and distributed a few along the axial. The distribution of the annular appeared in thecorresponding regions in the vorticity map, the center of the annular corresponds to the centerof the vortex, while the fluid particles revolve, but also from rotation. The vorticity is thecharacterization amount of the fluid particles revolve themselves. Nucleus rotation make thetemperature and concentration field is distributed uniformity, the semi-solid nucleus can formspherulities organization directly. The mutation zone of velocity and vorticity is the zones ofthe spherical crystal formed directly, the smooth area of the velocity and vorticity is thereunion area of the spherical crystal. In the case of changing the surface roughness, the flowfield was essentially the same by simulation, so the surface roughness has a smaller impact onthe outside of the boundary layer region, and has a certain effect on the regional boundarylayer; The simulation results are in accord with the experimental results of the sphericalcrystal direct formation mechanism, the cause of direct shear agitation spherical crystalformation is explained initially, providing a theoretical basis for the preparation of semi-solidslurry.