Transient Turbulent Flow in a Liquid-Metal Model of Continuous Casting,Including Comparison of Six Different Methods

Computational modeling is an important tool to understand and stabilize transient turbulent fluid flow in the continuous casting of steel to minimize defects. The current work combines the predictions of two steady Reynolds-averaged Navier–Stokes (RANS) models, a “filtered” unsteady RANS model, and two large eddy simulation (LES) models with ultrasonic Doppler velocimetry (UDV) measurements in a small-scale liquid GaInSn model of the continuous casting mold region fed by a bifurcated well-bottom nozzle with horizontal ports. Both mean and transient features of the turbulent flow are investigated. LES outperformed all models while matching the measurements, except in locations where measurement problems are suspected. The LES model also captured high-frequency fluctuations, which the measurements could not detect. Steady RANS models were the least accurate methods. Turbulent velocity variation frequencies and energies decreased with distance from the nozzle port regions. Proper orthogonal decomposition analysis, instantaneous velocity patterns, and Reynolds stresses reveal that velocity fluctuations and flow structures associated with the alternating-direction swirl in the nozzle bottom lead to a wobbling jet exiting the ports into the mold. These turbulent flow structures are responsible for patterns observed in both the time average flow and the statistics of their fluctuations.     

板坯连铸水口内钢液流动的数值模拟

 运用CFX计算软件研究了大通钢量工况下板坯浸入式水口流场,分析了水口结构、结晶器流动控制方式、水口吹氩等对浸入式水口流场的影响。研究表明,适宜的水口结构和控流方式组合能获得最优的水口出口流股形态和稳定均衡的流场。在大通钢量下,塞棒、底部凸起水口结构是最佳组合。不适宜的工艺组合形成并加重水口偏流,造成结晶器初始坯壳的不均匀冲刷和液面涡流,进一步诱发水口堵塞、水口结瘤、结晶器非稳态和不均衡传热,最终导致铸坯缺陷甚至诱发拉漏事故。     

MCCR产线110mm薄板坯结晶器流场的数值模拟

摘要：首钢京唐MCCR产线是国内第一条多模式连铸连轧产线,薄板坯高拉速连铸是实现无头轧制模式的基础,结晶器内流场控制是决定薄板坯高拉速连铸的关键。采用VOF两相流模型研究薄板坯连铸结晶器内流场特点,采用插钉法测量实际生产过程结晶器弯月面流速,并与对应工况条件下模拟结果进行对比校验了模型准确性。通过薄板坯连铸结晶器内流场的数值模拟仿真,获得了薄板坯高拉速条件下结晶器内钢液的流动特征。研究了连铸拉速、2.种浸入式水口结构等因素对弯月面流速以及波高差的影响。结果表明：随着通钢量由3.4t/min增加至8.2t/min,采用四孔水口时,结晶器弯月面钢液流速由0.02m/s增加至0.30m/s,结晶器钢液面波高差由2.0mm增加至7.2mm;采用五孔水口时,结晶器钢液面波高差由0.25m/s增加至0.5m/s,结晶器钢液面波高差由2.6mm增加至17.0mm。高通钢量条件下（5.5~8.2t/min）,采用四孔水口更加有利于控制液面波动稳定性。     

板坯连铸结晶器内钢液表面流速的水模型研究

以承德钢铁厂板坯连铸结晶器为原型,采用1∶1的水模型进行试验,研究了拉速、浸入式水口出口角度、水口浸入深度、水口底面结构及结晶器断面宽度等工艺参数对板坯结晶器内表面流速的影响。结果表明:拉速对表面流速的影响最大,随着拉速的提高,结晶器内钢液表面流速明显增大,当断面宽度为1 650 mm,拉速由0.7 m/min提高到1.4 m/min,表面流速由0.04 m/s提高到0.1 m/s;波浪面结构的浸入式水口表面流速效果最优。     

薄板坯连铸结晶器钢液流动数值模拟

以唐钢第一炼钢厂薄板坯连铸机为背景,利用商业模拟软件FLUENT,根据热轧薄板厂目前连铸操作的工艺参数,采用湍流模型建立数学模型,模拟了薄板坯连铸结晶器内钢液流场分布情况,系统地研究了水口结构、水口上出口倾角在指定拉速、浸入深度下对结晶器内流场的影响,为水口优化提供理论依据。在固定拉速和指定的浸入深度条件下,通过对比分析几种不同水口结构对结晶器内流场及温度场影响规律,最终确定采用五孔水口上出口倾角取15°为最佳水口结构方案。     

板坯连铸结晶器非稳态流场的模拟研究

本文运用数值模拟研究方法,研究高拉速厚板坯连铸非稳态结晶器流动特性,研究浸入式水口堵塞、水口不对中对结晶器流场、液面流速和对初生坯壳的影响。高拉速厚板坯连铸,铸坯质量下降,90%表面缺陷集中在铸坯边角区域,最严重的缺陷是铸坯中心和角部纵裂。非稳态工况对结晶器的流场影响因素更为显著,研究发现水口堵塞程度、水口出口流速、流量分配比是结晶器液面流速不对称、液面波动的主要影响因素,水口不对中是钢液流股对结晶器初生坯壳局部热冲击的主要因素,因此高拉速连铸应尽量避免非稳态工况操作,确保产品质量和效率的双赢。     

薄板坯连铸结晶器内涡流及卷渣行为的研究

利用1／4水模型对薄板坯连铸结晶器内的涡流及卷渣行为进行观察研究。在实验中考察了水口形状、水口浸入深度和浇铸速度等对漩涡及卷渣行为的影响,并考察了偏流以及在水口与结晶器宽面之问加翼片,阻止结晶器表面流股相互流动的漩涡（卷渣）现象。     

Vortex Flow Pattern in a Slab Continuous Casting Mold with Argon Gas Injection

An Eulerian-Eulerian two-fluid model was developed to study the vortex flow inside a slab continuous casting mold with argon gas injection. Interracial momentum transfer that accommodated various interracial forces including drag force, lift force, virtual mass force, and turbulent dispersion force was considered. Predicted results agree well vaith experimental measurements of the water model in two-phase flow pattern and vortex flow structures. Three typical flow patterns with different argon steel ratios （ASRs） have been obtained： ＂double roll＂, ＂three roll＂, and ＂single roll＂. The flow pattern inside the mold alternates among the three types or it may attain some intermedi ate condition. With increasing ASR, the positions of vortices move from the submerged entry nozzle to the narrow face of the mold, and the sizes of vortices are reduced gradually. The rotating directions of vortices are all from high velocity area to low velocity area. Two mechanisms of vortex formation on the top surface have been suggested, i. e. , congruous shear flow and incongruous shear flow.     

1 850 mm×230 mm板坯连铸结晶器流场与温度场数值模拟

为研究连铸工艺参数对结晶器内部钢液的作用规律,对涟钢1 850 mm×230 mm板坯连铸结晶器流场和温度场进行了系统的数值模拟,研究了不同吹氩量(0～7 L/min)、不同水口浸入深度(110～150 mm)和不同拉速(0.9～1.2 m/min)对结晶器内钢液行为的综合影响。结果表明,随着吹氩量增加,自由液面的钢液流速和温度总体呈现降低的趋势;随着水口浸入深度增加,自由液面的钢液流速先降低后增加;随着拉速增加,自由液面的钢液流速增加;水口浸入深度和拉速对温度场的影响较小。当吹氩量为5 L/min、水口浸入深度为130 mm、拉速为0.9 m/min时,结晶器自由液面具有较小的钢液流速和湍动能,同时液面具有较好的温度均匀性。通过数值模拟研究,为合理选择结晶器相关工艺参数提供了理论依据。     

薄板坯连铸结晶器三维流场和温度场的数值模拟

针对ＩＳＰ型薄板坯连铸结晶器，利用数值模拟的方法，计算结晶器的内流体的三维流场和温度场，比较和分析水口结构形状，插入深度及拉坯速度对结晶器内流场和温度场的影响，为薄板坯连铸结晶器以及相适应的伸入式水口结构形状选型提供参考。     

连铸结晶器内弥散氩气泡的瞬态运动和捕捉行为

针对连铸结晶器内弥散氩气泡的瞬态运动和捕捉行为,发展了耦合流动-传热凝固-气泡运动的大涡模拟模型,研究了结晶器凝固坯壳内钢液的非稳态湍流场和氩气泡的瞬态运动特征.结果表明,凝固坯壳对结晶器内钢液流场有较大影响,液相区内钢液流动不对称,导致气泡的运动和捕捉位置分布不均匀;小尺寸的气泡更容易运动到液相穴较深的区域;且随着拉...     

CSP结晶器内钢液流动的水模型研究

采用1:1水力学模型对厚度60 mm薄板坯连铸水口浸入深度220～310 mm、出口角度-30°～-60°、拉速4.2～6.0 m/min条件下CSP结晶器内钢液流动行为进行模拟研究。在拉速4.2～5.0 m/min时双侧孔水口下CSP结晶器流场股流冲击深度达850～1010 mm;流场内存在三个滞区,液面波动不稳定;水口角度对结晶器窄面和水口附近波动影响很显著,拉速对结晶器和窄面中心处波动影响较大,浸入深度对水口附近波动影响较大。     

中薄板坯连铸机结晶器的主要特点及其技术进步

介绍了薄板坯和中薄板坯连铸机结晶器的形状和主要特点,对比分析了不同类型结晶器内钢液的表面积、钢液流动、结晶器传热、薄板坯厚度、拉坯速度等对连铸过程和铸坯性能的影响,讨论了鞍钢ASP采用的先进技术,指出近年来新建和改造的薄板坯连铸机结晶器厚度呈现增加的趋势,从而解决了设备运行的一些问题,改善了铸坯质量。     

数值模拟开式水冷模铸机浇注过程

以南钢开式水冷模铸机为研究对象,建立了型腔内钢液三维非稳态流动、传热和液面波动的数学模型,研究了浇注过程中钢液的流动特征、温度分布以及注流卷吸气体的运动规律。结果表明：浇注过程中,在“气体卷吸”作用下,型腔内钢液的流动存在显著差异,浇注前期表现为上升流呈多个大小不一的涡旋流,浇注后期则呈典型的逆时针涡旋流,并充满整个模腔。在该流动行为影响下,型腔内钢液温度场表现为中心低四周高的系列等温带,钢液表面水平流速随液面高度的上升而增加,在液面高度为3.1 m时达到最大表面流速0.6 m/s ,此时液面波动大,易发生卷渣和钢液二次氧化。     

采用薄板坯连铸生产高表面质量冷轧钢板的可行性分析

薄板坯连铸由于拉速高,结晶器容量小,结晶器钢水液面波动高度和表面流速显著高于传统连铸,因此容易造成保护渣卷渣,这是薄板坯连铸生产高表面质量冷轧钢板钢种的主要困难所在。NUCOR、蒂森一克鲁伯等企业采用薄板坯连铸连轧工艺生产冷轧钢板的实践也表明,在表面质量方面与传统工艺产品尚有较大的差距。采用薄板坯连铸工艺生产优质冷轧钢种,应适当增加铸坯厚度,以降低拉速和增加结晶器对钢水流的缓冲作用,可采用120mm厚铸坯(结晶器出口),3m／min左右拉速。为了减少结晶器保护渣卷渣,应对中等厚度薄板坯连铸结晶器内钢水流动控制(SEN结构参数、SEN浸入深度、拉速等)、电磁制动、保护渣等开展深入的试验研究。     

Modeling of biased flow phenomena associated with the effects of static magnetic-field application and argon gas injection in slab continuous casting of steel

Biased flow occurs frequently in the slab continuous casting process and leads to downgraded steel quality. A mathematical model has been developed to analyze the three-dimensional biased flow phenomena associated with the effects of static magnetic-field application and argon gas injection in the slab continuous casting process. By moving the submerged entry nozzle (SEN) from center to off-center, the biased flow and vortexing flow in the mold can be reproduced in the numerical simulation. The existence of a vortexing flow is shown to result from three-dimensional biased flow in the mold. A vortex is located at the low-velocity side adjacent to the SEN. The vortex strength depends on the local horizontal velocity of molten steel and decreases gradually with distance from the free surface. The vortexing-zone size depends on the biased distance of the SEN, and the intensity of the vortexing flow depends on the casting speed of the continuous caster. Only when the location and strength of the magnetic field are properly chosen, can the vortexing flow be suppressed by a static magnetic-field application. The effect of argon gas injection on the vortexing flow is not remarkable. The combination of magnetic-field application and argon gas injection can correct the biased flow and suppress the vortexing flow by suppressing the surface velocity and removing the downward velocity near the SEN in the mold.     

Large Eddy Simulation of Turbulent Fluid Flow in Liquid Metal of Continuous Casting

The transient turbulent flow in continuous casting steel plays a key role in minimizing defects. Compared with the k-ε model, the large eddy simulation (LES) of turbulence provides much more accurate representation of turbulent flow by resolving large-scale dynamics. The turbulent flow in a liquid metal model of continuous casting has been simulated by LES and measured using ultrasonic Doppler velocimetry (UDV). The result of measurement and LES has been compared to validate the LES model and furthermore enhance the understanding of the transient turbulent feature in the flow field. The results show that the jet exiting from the nozzle port swings, which is not steady, and turbulent velocity variation frequencies decreased with distance from the nozzle port region and also the LES mode can capture the high frequency fluctuation, which the measurement cannot detect.     

Modeling of steel grade transition in continuous slab casting processes

Mathematical models have been developed and applied to investigate the composition distributions that arise during steel grade changes in the continuous slab casting processes. Three-dimensional (3-D) turbulent flow and transient mixing phenomena in the mold and the strand were calculated under conditions corresponding to a sudden change in grade. The composition distribution in the final slab was then predicted. Reasonable agreement was obtained between predicted and experimental concentration profiles in the slab centerlines. Intermixing in the center extends many meters below the transition point, while intermixing at the surface extends above. Higher casting speed increases the extent of intermixing. Mold width, ramping of casting speed, and nozzle design have only small effects. Slab thickness, however, significantly influences the intermixing length of the slab. The axial transport of solute due to turbulent eddy motion was found to be many orders of magnitude greater than molecular diffusion and thus dominates the resulting composition distribution. Different elements, therefore, exhibited the same mixing behavior under the same casting conditions, despite having different molecular properties. Numerical diffusion caused by the finite difference schemes was investigated and confirmed to be much less important than turbulent diffusion. In the lower portion of the strand (lower than 3 m below the meniscus), the convection and diffusion can be reasonably approximated as one-dimensional (1-D) axial flow.     

FTSC薄板坯连铸结晶器流场数值模拟

利用商业软件GAMBIT和FLUENT，针对FTSC薄板坯连铸结晶器，建立三维有限体积模型，用来描述结晶器内钢液流动特征。在此基础上，分析了浸入深度、拉坯速度以及水口倾角等参数对结晶器流场的影响，为FTSC薄板坯连铸结晶器相适应的浸入式水口结构尺寸优化提供参考。     

薄板坯连铸用平头浸入式水口的研究开发

通过研究薄板坯连铸机大通钢量条件下结晶器内钢水的流动特性,分析了浸入式水口出口射流对熔池温度分布、结晶器内液面波动等的影响。唐钢研发的一种薄板坯连铸机用平头浸入式水口,优化了浸入式水口钢液出钢孔端面的形状结构和在结晶器内的浸入深度,使高温钢水覆盖了整个结晶器表面,有利于保护渣的融化,解决了薄板坯连铸机拉速提高对结晶器流场、铸坯质量等方面的影响。