Large eddy simulation on the multiphase fluid flow and slag entrainment in a continuous casting mold with electromagnetic stirring
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摘要: 針對大方坯連鑄結晶器內的流動和卷渣行為進行了三維數值模擬仿真，應用大渦模擬模型模擬湍流、應用VOF模型模擬渣相?鋼液和空氣?渣相?鋼液的多相流。研究對比了鋼液單相流動、渣相?鋼液兩相流動和空氣?渣相?鋼液三相流動3種模型下結晶器內的流動、鋼?渣界面液位形狀和波動及卷渣行為，并通過工業用計算機斷層成像技術（工業CT）檢測了連鑄坯中大顆粒卷渣類夾雜物數量隨著電磁攪拌電流強度的變化。結果表明，在150 A、2 Hz結晶器電磁攪拌下，3種模型得到的結晶器內鋼液流場差別較小，但在鋼?渣界面處差別較大。鋼液單相模型下鋼液表面流動速度比其他兩種模型鋼?渣界面處的速度更大。渣相?鋼液兩相模型和空氣?渣相?鋼液三相模型的卷渣速率分別為0.00118和0.00040 kg?s?1。渣相?鋼液兩相模型條件下，由于上表面即渣的頂面不能彎曲，所以鋼?渣界面處的湍動能沒有得到耗散，所以比三相模型的湍動能更大，因此其預測的卷渣速率偏大。當攪拌電流強度增大到300 A，渣相?鋼液兩相模型和空氣?渣相?鋼液三相模型的卷渣速率分別為150 A條件下的5倍和15倍；當電流頻率增大到4 Hz，渣相?鋼液兩相模型的卷渣速率變化很小，空氣?渣相?鋼液三相模型的卷渣速率降低為2 Hz條件下的1/3。因此，為了正確的模擬和預測結晶器鋼?渣界面處的卷渣行為，必須使用空氣?渣相?鋼液三相瞬態模型進行模擬仿真。Abstract: Due to the closed environment with high temperature and pressure in the continuous casting (CC) process, numerical simulation technology with flexible control and low cost of phenomena in the CC mold has been a research hotspot. The multiphase flow, heat transfer, solidification of steel and slag, and other complex interaction in the mold are some of the simulation difficulties. Various physical models have been established in recent studies to obtain the reactions and effects of the different phases. However, the influence of different models on the simulation results is rarely studied. In the current study, a three-dimensional (3D) mathematical model, coupled with the large eddy simulation (LES) turbulent model and volume of fluid (VOF) multiphase model, was established to investigate the multiphase flow, slag-steel interface level fluctuation, and slag entrainment in the mold of a steel bloom CC with mold electromagnetic stirring (M-EMS). The air?slag?steel three-phase flow, slag?steel two-phase flow, and steel single-phase flow were compared. An industrial computerized tomography (CT) was used to detect the large entrainment slag inclusions in blooms with different stirring current intensities. With a 150-A current intensity and a 2-Hz frequency electromagnetic stirring at the mold, the multiphase flows are approximately identical for the three models, although different at the slag?steel interface. The speed on the top surface of the single-phase model is higher than that of the multiphase models. The level fluctuation of the two-phase model is slightly more severe than that of the three-phase model, and the net slag entrainment rates of the two-phase and three-phase models are 0.00118 and 0.00040 kg·s?1, respectively. The turbulence kinetic energy at the slag?steel interface of the two-phase model is significantly greater than that of the three-phase model because the turbulence kinetic energy can not be dissipated, unlike that in the actual process. Thus, the predicated slag entrainment obtained by the two-phase model is higher. On increasing the stirring current intensity to 300 A, the net slag entrainment rate is 5 times and 15 times higher for the two-phase and three-phase model higher than that under 150 A; when the current frequency increases to 4 Hz, the net slag entrainment rate of the two-phase model varies little, while that of the three-phase model becomes 1/3 of that under 2 Hz. To accurately simulate and predict the slag entrainment phenomena at the CC mold, the air?slag?steel three-phase multiphase model should be mandatory.
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圖 1 空氣?渣相?鋼液三相模型的物理模型尺寸和網格設置
Figure 1. Schematic of physical model size and mesh distribution of the steel?slag?air three-phase model
圖 2 電磁攪拌位置示意圖及模型驗證. (a) 電磁攪拌安裝位置示意圖; (b) 結晶器中心線處磁通密度測量值與計算值的對比
Figure 2. Diagram of the M-EMS installing location and model validation: (a) M-EMS installing location; (b) magnetic flux density along the mold center vertical direction
圖 3 結晶器垂直中心線上的電磁力分布
Figure 3. Distribution of the electromagnetic force along the vertical distance below the meniscus
圖 4 時均速度大小分布. (a)鋼液單相模型; (b)渣相?鋼液兩相模型; (c)空氣?渣相?鋼液三相模型
Figure 4. Distribution of time-average velocity magnitude: (a) steel?slag single-phase model; (b) steel?slag two-phase model; (c) steel?slag?air three-phase model
圖 5 監測點P點處鋼液3個方向上的脈動速度
Figure 5. Steel fluctuation velocity in different directions at monitored point P
圖 6 彎月面時均速度分布. (a)鋼液單相模型; (b)渣相?鋼液兩相模型; (c)空氣?渣相?鋼液三相模型; (d) 彎月面在結晶器厚度中心線上的流動的速度大小
Figure 6. Time-average speed distribution of the meniscus: (a) steel?slag single-phase model; (b) steel?slag two-phase model; (c) steel?slag?air three-phase model; (d) time-average velocity magnitude along meniscus width center line
圖 8 不同監測點處的液面波動. (a) P1; (b) P3
Figure 8. Surface fluctuations at different monitoring points: (a) P1; (b) P3
圖 9 通過Z=0.04 m平面的凈渣相質量
Figure 9. Net slag mass through the horizontal plane of Z=0.04 m below the mold top surface
圖 10 鋼?渣界面的湍動能分布. (a) 渣相?鋼液兩相模型; (b) 空氣?渣相?鋼液三項模型
Figure 10. Turbulence kinetic energy distribution on steel/slag interface: (a) steel?slag two-phase model; (b) steel?slag?air three-phase model
圖 11 鋼?渣界面寬度中心線. (a) 液面瞬時位置; (b) 湍動能值
Figure 11. Along steel/slag interface: (a) surface transient level position; (b) turbulence kinetic energy
圖 12 電流300 A,頻率 2 Hz的電磁攪拌條件下彎月面寬度中心線處時均速度
Figure 12. Time-average velocity magnitude along meniscus width center line
圖 13 不同電流強度下通過Z=0.04 m平面的凈渣相質量
Figure 13. Net slag mass through the horizontal plane of Z=0.04 m below mold top surface under different current densities
圖 14 150 A, 4 Hz下彎月面寬度中心線處時均速度大小
Figure 14. Time-average velocity magnitude along meniscus width center line under 150 A current intensity and 2 Hz frequency
圖 15 不同電流頻率下通過Z=0.04 m平面的凈渣相質量
Figure 15. Net slag mass through the horizontal plane of Z=0.04 m below mold top surface under different current frequency
圖 16 不同電流強度下的夾雜物形貌. (a) 100 A; (b) 300 A; (c) 600 A
Figure 16. Morphologies of slag entrainment inclusions with M-EMS of different current intensities: (a) 100 A; (b) 300 A; (c) 600 A
圖 17 不同電流強度下卷渣類夾雜物的體積分數
Figure 17. Volume fraction of inclusions from slag entrainment in the CC bloom varied with different current intensities M-EMS
表 1 模型尺寸及物性參數
Table 1. Model dimensions and material parameters
Parameters Value Parameters Value Submergence depth of SEN/ mm 120 Molten steel density/（kg·m?3） 7020 Mold length/ mm 800 Molten steel viscosity/ （kg·m?1·s?1） 0.0055 Air phase thickness/ mm 65 Superheat of molten steel/ K 20 Slag phase thickness/ mm 35 Slag density/（kg·m?3） 2500 Radius of curvature/ m 10.25 Slag viscosity/（kg·m?1·s?1） 0.18 Section size/（mm×mm） 280×250 Liquidus temperature of molten steel/ K 1727 Casting speed/（m·min?1） 0.62 Surface tension of molten steel/（N·m?1） 1.6 M-EMS parameters 150 A，2 Hz
300 A，2 Hz
150 A，4 HzTotal length of domain/ m 2 
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