Three-Dimensional Modeling for Estimation of Hydraulic Retention Time in a Reservoir

A three-dimensional computational fluid dynamics model is used to estimate the hydraulic residence time for a portion of the Wachusett Reservoir in central Massachusetts. The basin under consideration has several major inflows and exhibits complex flow patterns. The basin is modeled using the FLUENT software package with particles used to track travel time in a steady-state flow field. A tetrahedral mesh with over 1.6 million cells is used with accurate depiction of basin bathymetry and inlet and outlet geometries. Modeling is performed to simulate behavior during a period when conditions are isothermal. It is determined that mean hydraulic residence time is 3–4?days; approximately half of what would be expected assuming strictly plug flow. The presence of a primary flow path, large scale eddies and stagnation zones contribute to the faster travel times. Reductions in inflow rates produce increased residence times and significant changes in flow patterns.     

基于PMV的矿井独头巷道通风效果分析

矿井独头巷道内高温环境日益严重,根据传热学和流体力学理论,应用F luent软件对某深井独头巷道内的通风风流速度场、温度场进行模拟,并利用预测平均热感觉指标PMV对通风效果进行评价.结果表明:独头巷道通风风流结构分为射流区、回流区及涡流区,其中涡流区流速最小,换气效率最差;利用M atlab进行计算,得出PMV值范围为0.7~1.7,热感觉评价等级为稍暖,该结果与实际情况吻合.PMV值受巷道内空气温度、速度影响较大,在巷道中间高度位置(y=1.5 m)处,由于涡流的存在,风速较小,换气效率差,空气温度高,导致PMV偏大,因此,提高矿工热舒适性首先要考虑控制好巷道内空气温度及流速.     

高温高压喷射条件下X70管线钢的CO2腐蚀形貌

利用自主研发的高温高压环路喷射装置并结合流体动力学模拟计算,研究了高温高压CO₂环境流体喷射条件下X70钢的腐蚀产物微观形貌、基体表面三维形貌、腐蚀减薄量及其统计规律,并探讨了与流体状态之间的关系.结果表明,高温高压流体喷射条件下,不同流态区域内流体传质速率和壁面切应力的差异是造成X70钢腐蚀产物、基体表面三维形貌及腐蚀减薄量差异的主要原因.按照层流区→壁面喷射区→过渡区的顺序,流体壁面切应力逐渐增加,不断减薄腐蚀产物膜直至其脱落,造成传质过程阻力减小,传质速率增大,腐蚀过程不断加剧.因此,按照层流区→壁面喷射区→过渡区的顺序,X70钢表面腐蚀产物膜由完整致密向疏松多孔变化,基体表面三维形貌呈现平坦→陡峭→非常陡峭的特征,三维表面高度偏差和均方根偏差、腐蚀减薄量平均值和标准差均呈现逐渐增大的趋势.在高温高压流体喷射条件下,X70钢的CO₂腐蚀速率与壁面切应力之间较好地满足指数关系.      

Near-Field Mixing Downstream of a Multiport Diffuser in a Shallow River

Near-field mixing downstream of a multiport diffuser in a wide shallow river was studied with a field dye test. Dye concentrations at different depths and lateral locations were measured. The near-field mixing was analyzed in four zones: the free jet zone, the jet surface-impingement zone, the merging zone, and the vertical mixing zone. Analytical models were proposed to derive the three-dimensional concentration field after the jets impinged the water surface. After the impingement, the dye concentration can be predicted well by treating the multiple jets as a simple mathematical summation of individual jets. The vertical mixing zone was dominated by the riverbed friction-induced turbulence, with little effect from the effluent momentum and buoyancy. The results of the field data were also used to validate the applicability of some existing models for multiport diffusers.     

立式电磁制动对不同水口角度下连铸结晶器内流场的控制

利用Fluent软件模拟计算了常规板坯连铸和立式电磁制动板坯连铸过程,详细研究了不同水口出口角度结晶器内三维流场,为评价立式电磁制动技术的冶金效果提供理论依据.研究表明:常规连铸过程水口出口角度增加时,不利于夹杂物的上浮,影响铸坯质量;不同水口出口角度连铸过程应用立式电磁制动技术后,自由表面钢液流速、钢液主射流的运动速度和下回流区的冲击深度显著减小,利于稳定液面波动、减少卷渣、防止漏钢和促进夹杂物的上浮,符合立式电磁制动技术的设计思想.     

50 t转炉四孔变角氧枪射流融合距离的数值模拟

采用Fluent软件模拟了50 t转炉四孔变角和非变角氧枪气体射流,研究了喷孔倾角对氧气射流流场和流股融合距离的影响。结果表明,在距喷头出口距离较近时,各流股独立为自由射流,随着距喷头出口距离的增加,各流股不断扩张,并在一定距离时融合成单股射流;非变角喷头A的流股融合距离为1.3 m,与冷态水模实验得出枪位1.3 m时炉口溅出量最大是一致的;变角氧枪B至I的对角喷孔倾角不同,射流流股融合了两次,大大降低了炉口溅出量;变角氧枪对角喷孔倾角相差0.5°较对角喷孔倾角相差1°时更有利于射流融合距离的增加;在研究喷孔倾角10.5°~11.5°/12.5°的9个喷头中,倾角11°/11.5°的喷头H射流融合距离最长,其理论炉口喷溅量最少。     

Numerical Simulation of Fluid Flow in a Round Bloom Mold with In-Mold Rotary Electromagnetic Stirring

In this article, an electromagnetic field simulation and a flow analysis model are performed to describe the three-dimensional electromagnetic field distribution and the electromagnetically driven flow characteristics in a round-bloom mold with a low-frequency in-mold rotary electromagnetic stirrer. The interaction between the induced flow and the inertial impinging jet from a straight-through submerged entry nozzle (SEN) of the caster is considered. The effects of stirrer current and frequency on the electromagnetic field and the flow in the round-bloom mold are investigated, and a strategy to optimize the stirring parameters is proposed. The results show that the distributions of magnetic flux density and electromagnetic force magnitude are nonuniform in a three-dimensional electromagnetic stirring (EMS) configuration. There exists a significant axial induced component of electromagnetic force. The flow in the in-mold EMS system is characterized by a dominant swirling movement at the transverse sections, coupled with the recirculating flows in the axial direction. An upper recirculation zone and a lower recirculation zone with the reverse melt flowing are found near the strand wall at the axial location close to the middle of the stirrer, and another recirculation zone is formed due to the interference of the induced flow with the jet from SEN. The meniscus surface has a swirl flow, and the meniscus level rises near the bloom strand wall and sinks around the SEN wall. All of these flow features are closely associated with metallurgical performances of the in-mold rotary stirrer. With the increase of stirring current and the decrease of frequency, the magnetic flux magnitude increases. There is an optimum frequency to obtain a peak of electromagnetic force magnitude and maximum tangential velocity. For a mold rotary EMS system, to determine the optimum stirring intensity, it is necessary to make a compromise between a larger tangential velocity and a relatively quiescent meniscus surface.     

Field Measurements of Mean Velocity Characteristics of a Large-Diameter Swirling Jet

Full-scale field acoustic Doppler velocimeter measurements of the radial, axial, and tangential flow components were undertaken in a large-diameter turbulent swirling jet generated by a raft-mounted axial flow-mixing propeller discharging through a draft tube during isothermal and stratified conditions. The results were compared with classical jet theory and showed significant differences in the zone of flow establishment though similar behavior in the zone where established flow was found. It was concluded that the efflux from the axial flow-mixing propeller could not be described adequately by conventional jet theory due to the jet size and swirling characteristics.     

喷嘴射流特征对连铸二冷区蒸汽膜穿透行为的影响

 连铸二冷区铸坯表面温度通常高于900 ℃,此时喷淋液滴接触高温铸坯时不会湿润铸坯表面,仅在其上形成一层蒸汽膜,阻碍了液滴与铸坯表面接触传热。针对以上问题,以国内某钢厂连铸二冷区的扁平型水喷嘴为原型,建立了喷嘴射流仿真计算模型,并对所建模型进行了理论和实验室验证;采用数值模拟的方法研究了喷嘴自由射流区的流场分布,运用连铸喷嘴冷却检测系统测量获得了射流液滴粒径演变规律;结合数值模拟和实验室测定结果,定量分析了喷嘴在不同水流量下射流液滴冲击铸坯表面蒸汽膜深度的变化规律。结果表明,该喷嘴的最大射流速度在喷嘴出口处,射流在喷嘴出口附近出能维持较大的射流速度,且随着水量的增加,射流保持高射流速度的距离也增长;整体射流的轴向速度占比均在80%以上。当喷淋水量越大时,射流液滴粒径变得越小;随着距喷嘴出口距离的增加,射流中心处的液滴粒径逐渐增大并达到最大值;当水流量为9和12 L/min时,液滴粒径基本相同,这表明当水流量增加到一定值时,冷却水量的增加不影响液滴粒径分布。在不同水流量下,随着喷淋距离的增加,液滴穿透铸坯表面蒸汽膜深度呈先增大后略微减小的变化规律,在喷射距离为100~200 mm范围内时,液滴穿透深度最大,这表明喷射高度在该范围时,喷淋冷却效果最好。     

Interfacial Fluctuation Behavior of Steel/Slag in Medium-Thin Slab Continuous Casting Mold With Argon Gas Injection

 The flow field of molten steel and the interfacial behaviour between molten steel and liquid slag layer in medium-thin slab continuous casting mold with argon gas injection was studied by numerical simulation, in which the effects of nozzle submergence depth and port angle, casting speed, and argon gas flow rate on the flow and the level fluctuation of molten steel were considered. The results show that the molten steel jet from the submerged entry nozzle (SEN) with three ports into the mold and form three re-circulation zones including one upper re-circulation zone and two lower re-circulation zones. Argon gas injection results in a secondary vortex flow in the upper zone near the nozzle. For a given casting speed and argon gas flow rate, increasing the side port angle and submergence depth of nozzle can effectively restrain the steel/slag interfacial fluctuation. Increasing the casting speed would prick up the level fluctuation. For a fixed casting speed, argon gas flow rate has a critical value, the interfacial fluctuation with argon gas injection are stronger than the case without argon gas injection when the argon gas flow rate is less than the critical value, but when the argon gas flow rate exceeds the critical value, the level fluctuation is calmer than that without argon gas injection.     

四流中间包流场影响因素分析与优化

采用正交试验法建立1:2.5水力学模型,选取L12(22×31)混合正交表设计12组水模试验方案,对水模试验结果进行极差分析,分析挡墙类型、挡墙导孔孔径和挡墙导孔倾角对中间包流场特性的影响大小,并找出合理的控流装置配置.结果表明,挡墙导流孔倾角对中间包流场特性影响最大,其次是导流孔孔径和挡墙类型.采用Y型挡墙,挡墙导孔...     

Mean Flow Field of a Nonbuoyant Rectangular Surface Jet

The flow field for a low Froude number nonbuoyant rectangular surface jet is studied using laser induced fluorescence and laser Doppler velocimetry. It is shown that a surface current develops in turbulent, but not in laminar jets. The existence of a self-similar regime is established. The lateral growth rate of the jet below the surface is about 4.8 times its vertical growth rate, while that of the surface current is 8.8 times. The vertical growth rate is about half that of a plane surface jet and less than one third that of a free axisymmetric jet. While the horizontal profiles of the streamwise velocity are similar to those observed in free, submerged, and wall jets, the vertical distributions are distinctly flatter.     

Physical and mathematical models of gas‐liquid fluid dynamics in LD converters

Fluid dynamics of gas‐liquid interactions in a LD converter to refine steel was physically and mathematically simulated. Using a water model three cases of gas supply were considered, top blowing, bottom injection and combined process top blowing‐bottom injection. Mixing time in top blowing increases with bath height and the distance between the lance of the gaseous jet and the bath surface. The jet penetration was found to be dependent on the modified Froude number. The unstable and unsteady behaviour of the bath topography, as affected by the gaseous jet, was well simulated through a multiphase momentum transfer model. In top blowing, three zones of liquid splashing were found, penetration with low splash, heavy splash and dimpling with low splash intensity. These zones depend on the gas flow rate and the distance from the lance to the bath surface. During bottom injection mixing times decrease with the number of tuyères, increases of bath height and gas flow rate. In a combined process mixing time decreases considerably due to the recirculating flow formed by the action of the top jet and the submerged jets. When a submerged jet is located just below the top jet the mixing time does not decrease as compared with the separated processes either top blowing or bottom stirring.     

To the problem of steel desulfurization in a ladle-furnace unit and a chamber degasser

The laws of deep steel desulfirization in a ladle upon treatment in a ladle-furnace unit and after degassing are considered. On the basis of experiments, a mechanism is proposed for extraction refining by slag with allowance for the role of drop formation in the zone of gas jet outlet. The mechanism consists of several consecutive stages. Under vacuum, the process of stirring with an inert gas substantially enhances the desulfurization rate and can be restricted only by too intense steel cooling and in the absence of a free wall margin in a steel-teeming ladle.     

RH熔池内弱搅拌区特性的模拟研究

以某钢铁厂170 tRH精炼装置为原型,运用数值模拟的方法对其在不同吹气量、浸渍管内径、插入深度和真空度下的流场进行了模拟,并对熔池内弱搅拌区的分布和变化进行了分析。研究表明:大包熔池上部存在3个弱搅拌区。随着吹气量的增大,1区、3区区域迅速减小;2区先增大后减小,在100 m3/h时达到最大。增大浸渍管内径,1区、2区、3区区域减小,2区在两浸渍管中下方出现了一狭长的弱搅拌区。增大浸渍管插入深度,3个弱搅拌区增大,熔池液面处速度降低,趋于平稳。增大真空度,3个弱搅拌区略有减小。在降低弱搅拌区的几个因素中,吹气量影响最大,浸渍管内径次之,真空度最小。     

Numerical Prediction on the Flow Field of Molten Steel and the Trajectory of Inclusion in Continuous Casting Mold Effected by Electromagnetic Field

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水口类型对大方坯结晶器内钢水流动与凝固行为的影响

采用数值计算方法对比研究了直通式、4分径向以及新型4分切向水口对大方坯连铸结晶器内钢水流动与凝固行为的影响.结果表明,当前常用的直通式水口对坯壳无冲击,利于坯壳均匀生长,但钢水冲击深度大,易在弯月面处形成死区,不利于大方坯内部及表面质量的提高;改用4分水口浇铸时,结晶器宽、窄面冲击区附近都会出现不同程度的坯壳厚度零增长...     

Effect of Thermal Buoyancy on Fluid Flow and Inclusion Motion in Tundish without Flow Control Devices--Part Ⅰ: Fluid Flow

The κ-ε two-equation model is used to simulate the fluid flow in the continuous casting tundish coupling with the effect of thermal buoyancy. The natural convection induced by the thermal buoyancy generates an upward flow pattern especially at the outlet zone, and has little effect on the fluid flow in the inlet zone. The maximum viscosity is 700 times larger than the laminar viscosity, which indicates the strong turbulent flow in the tundish. The maximum temperature difference in the whole tundish is 8.2 K. The temperature near the stopper rod and the short wall is obviously lower than that in the inlet zone. The existence of the stopper rod has a big effect on the fluid flow entering the SEN and the mold. All the characteristics of the tundish geometry should be considered to accurately simulate the fluid flow in the tundish.     

Fluid Mechanics of Triangular Sediment Oxygen Demand Chamber

Benthal respiration rates are often measured in situ by a sediment oxygen demand (SOD) chamber in which a continuous flow is generated above the sediment. The steady three-dimensional turbulent flow field inside a triangular SOD chamber (previously used in field investigations) is computed using the renormalization group (RNG) k–ε model on an unstructured tetrahedral mesh. The numerical predictions reveal a highly complicated flow characterized by (1) a jet flow near the level of the inlet, with strong downflow near the outlet end; (2) significant reverse bottom currents; and (3) strong secondary circulations in the triangular cross section. Good mixing is achieved, with mean near-bottom velocities about 10 times greater than that determined from the inflow discharge and cross-sectional area. The computed velocity field is well supported by laboratory velocity measurements using laser-Doppler anemometry (LDA). The implications on SOD chamber design are also discussed with reference to computed flow fields in representative dome-shaped and rectangular chambers used in field application. The present study explains the previous large discrepancies in SOD field measurement using chambers of different designs, and points to the importance of hydrodynamics of SOD chambers.     

前混合磨料水射流除鳞喷嘴混合腔内部流场

基于计算流体动力学多相流混合物模型,应用FLUENT软件对前混合磨料水射流除鳞喷嘴高压水与磨料混合腔内部流场进行数值模拟.比较了不同进料方式对流场均匀性的影响.分析了两侧为高压水入口条件下,磨料入口直径、高压水入口直径、高压水入口位置和角度以及收缩段锥角对流场混合均匀性的影响,得到了影响混合腔内部流场混合均匀性的合理结构参数.数值计算结果表明:入口速度一定的条件下,磨料中进式喷嘴混合腔的混合均匀性优于磨料侧进式喷嘴混合腔.随磨料入口和高压水入口直径增加,混合腔出口的射流速度均增加,但随高压水入口直径增加导致出口磨料浓度呈先增后减的趋势,磨料入口与高压水入口合理的质量流量比值约为3∶4,两侧高压水入口位置对流场混合均匀性影响较小,高压水入口角度和收缩段锥角均为30°时流场性能更佳.