Large Eddy And RANS Simulation For Flow And Heat Transfer With EMBr In CSP Thin Slab Continuous Casting Mold

In this dissertation, how the flow field, temperature field in a thin slab mold change with casting speed, width of cross-section,submerged depths,current of the Electromagnetic Brake(EMBr) were studied through the two model methods of numerical simulation by taking the Compact Strip Production(CSP) continuous casting process of the Lianyuan Steel as archetype.There are four parts in this paper. Firstly, the flow field and temperature field in the mold without EMBr are calculated by using the model of Reynolds-averaged Naiver Stokes(RANS). The results show that, without EMBr, the steel liquid jet from the Submerged Entry Nozzle(SEN) has a larger impact on the narrow side of mold that worsen the growth of solidified shell. Meanwhile the center of upper flow is close to the surface which may aggravate surface flow fluctuation and slag entrapment.Subsequently, the flow field and temperature field in the mold with EMBr were calculated by using the method of RANS model. The results showed that, with EMBR, the electromagnetic brake can significantly optimize the flow in the mold by slowing down the steel flow, depressing the compact of flow on narrow side of mold, reducing the velocity and improving the temperature of the mold meniscus. For the 920 mm mold and 120 mm immersion depth of the SEN and 5.1m/min casting speed, with EMBr, the velocity on the meniscus can be reduced by about 14%, and its temperature can be increased by 5oC. At the same time, the electromagnetic brake can also increase the flow stream and heat flux to upper mold, which improve the activity of meniscus and enhance the effect of smelting of the mold slag on the meniscus. In addition, based on the principle of electromagnetic brake, the electromagnetic brake can only play a role in the flow of cutting magnetic line by reducing the molten steel speed, and has no effect on the flow along the parallel direction. The electromagnetic braking force varies directly as the current value and the fluid flow velocity, also, the force would increase when the position of the submerged nozzle is closer to the core of the magnetic field.In the third part of this paper, the flow field and vorticity field in the mold are calculated by using the method of Large Eddy Simulation(LES). The results show that the flow in the mold belongs to a strong turbulent flow, which has characteristic of turbulence, so the flow in the mold is asymmetric flow, and the asymmetry would intensify with the increase of the casting speed. The flow pattern under the SEN in the CSP mold contains three kinds of typical forms: "left rotation"(counter-clockwise), "right rotation"(clockwise) and "double rotation". The generation of vorticity is due to the condition of wall adhesion, and the vortex gradually dissipated with the flow develops forward. Electromagnetic brake has an important influence on vorticity dissipation. A stronger magnetic field is beneficial to the vorticity dissipation in a short distance. The EMBr can reduce the asymmetry of mold flow, but cannot eliminate it.Finally, the characteristics of Large Eddy Simulation method and the Reynolds time-averaged method are compared from three aspects: the subgrid filter length, the dissipation of vorticity of center plane, the dissipation of vorticity of various section along the height of mold. The results show that the RANS method can only provide the results of the average motion, while the LES method can provide more real results, which is consistent with the simulation results of the 1:1 ratio water model, and the accuracy of the calculation is related to the size of the subgrid filter length.