聚合射流流场的仿真模拟

 为研究有低密度伴随的聚合射流氧枪射流流场,利用氧枪射流检测系统,对常温下(冷态)以空气模拟的射流进行了物理模拟。结合数值模拟结果,分析了传统无伴随流射流以及带有副孔氦气低密度伴随情况下射流流场的流动状态,讨论了在不同的滞止压力和环境温度时有、无伴随射流流场特性。结果表明,修正的k ε双方程模型能较好地预测实验结果,伴随流的存在减缓了中心射流的沿程衰减,环境温度的变化影响射流在径向和轴向的流动状态。     

聚合射流氧枪射流特性的实验研究

利用带有中心主孔的Laval喷管和16个副孔的聚合射流氧枪喷头的氧枪射流检测系统研究氧枪射流中心速度的衰减规律,测试常温氦气代替高温燃烧的保护气体作为伴流而产生的聚合射流,以及高温以主孔通空气,两副孔分别通入氧气和丙烷来产生保护气体模拟的聚合射流。结果表明,聚合射流特性优于传统射流特性,常温下随氦气入口压力增加,中心射流的轴向衰减变缓,获得比传统超音速射流更长的超声速区域;高温下通过调节燃气和氧气流量可改变环状火焰长度,同时可以根据生产实际情况变化主射流长度,满足冶炼工艺要求。     

环境温度对超音速氧气射流特性影响的数值模拟

通过数值模拟的方法研究了不同环境温度条件下超音速氧气射流的特性,并与前人的实验结果进行了对比分析.研究结果表明:与低温环境条件相比,高温环境条件下超音速氧气射流的速度衰减受到抑制,射流核心段长度得到延长;不同环境温度条件下,氧气射流的温度随着氧气射流的扩散不断升高,最终趋于环境温度;射流的压力分布趋势与射流速度分布趋势一致.数值模拟得到的射流速度、温度和压力结果与实测值吻合度较高.      

环境压力对超音速氧气射流特性影响的数值模拟

超音速氧气射流技术是炼钢精炼过程中的重要环节,关于常压条件下超音速氧气射流的特性已进行了大量的研究,但对真空精炼过程中低压环境下的超音速氧气射流特性目前研究较少。通过数值模拟的方法研究了不同环境压力条件下超音速氧气射流的特性,并与试验结果进行了对比分析。研究结果表明：低压环境条件与高压环境条件相比,超音速氧气射流速度的衰减受到抑制,射流核心段的长度得到延长;不同环境压力条件下,射流压力与射流速度分布趋势一致,均沿轴向不断降低,但压力衰减程度大于速度衰减的程度;不同环境压力条件下,氧气射流的温度随着氧气射流的扩散不断升高,最终趋于环境温度。     

超音速氧枪射流特性的数值模拟

利用GAMBIT建立了轴向计算长度2 200 mm和径向计算长度800 mm的超音速氧枪的数学模型,并采用FLUENT软件对氧枪射流特性进行数值仿真研究。分析了单孔氧枪超音速射流特性,以及操作压力(0.6~1.0 MPa)和环境温度(298~1 873 K)对流动特性的影响。结果表明,入口滞止压力在设计压力±25%内对射流轴向衰减及径向扩展影响不大,其与射流的超音速区长度呈二次曲线关系变化,随环境温度升高,射流轴向衰减变缓慢,核心区长度增加,超音速区长度和环境温度呈线性关系,环境温度对射流径向影响很小。     

氧气炼钢过程中超音速射流湍流特性的实验研究

用DISA热线风速仪研究了氧枪射流中心轴线上和横截面上脉动速度、湍流强度以及自相关系数的变化规律。实验结果表明,在射流中心轴线上,脉动速度随着距喷嘴出口的距离增加而衰减,湍流强度在H/d_e≥20～25以后保持不变;在与射流中心轴线的半锥角为1°的圆锥面上,脉动速度为最大,在9.25°的圆锥面上湍流强度最大;在射流的横截面上,自相关系数为一常数。这些结果为探讨LD转炉和VOD等吹炼过程中氧气射流与熔池作用,以及氧枪的设计和操作提供了参考。     

基于环境温度的转炉旋流氧枪射流分析

为探究旋流氧枪自由射流特性,建立了0°、6°、12°和18°旋流氧枪自由射流几何模型,分析了不同旋流氧枪炼钢温度下的旋流特性、射流速度和动压分布。发现与0°旋流氧枪相比,6°、12°和18°旋流氧枪射流速度和动压衰减较快,且旋流角越大,射流衰减越快。而6°旋流氧枪与12°和18°旋流氧枪相比,射流速度和动压衰减较慢,在保证合适冲击深度和冲击面积的同时,使熔池产生一定的旋转运动。基于此,建立了6°旋流氧枪和转炉气-渣-金多相流几何模型,分析了环境温度变化对6°旋流氧枪冲击特性和熔池速度分布的影响,发现环境温度从300 K升高到1 873 K,冲击半径从1.25 m增至1.78 m,而冲击深度仅从0.119 m增至0.132 m。环境温度升高,钢液面处高速区面积增大,死区和低速区面积减小;在熔池较浅处,环境温度升高,熔池死区面积减小,高速区面积增大,以熔池深度0.3 m为例,环境温度从300 K升高到1 873 K,死区面积由0.41 m²减小至0.17 m²,高速区面积由9.35 m²增至9.76 m²     

200 t转炉交错氧枪设计优化研究

以200t转炉5孔氧枪为原型,优化设计内外喷孔相同倾斜角度下不同流量配比的交错氧枪.基于射流特性仿真研究,通过数值模拟方法,分析交错氧枪喷头射流特性与传统5孔氧枪的不同,探讨内外孔流量比变化对氧枪射流轴向速度衰减和有效冲击面积的影响规律.结果 表明:交错氧枪内孔射流轴向速度大于传统氧枪,外孔的轴向速度与传统氧枪相近,但...     

氧气炼钢过程中射流对熔池的作用

本文总结了用模型实验研究顶吹氧气转炉炼钢过程中超音速氧气射流的特性及其对熔池作用的某些问题。应用相似原理进行实验室研究,得出超音速氧气射流轴线上速度衰减,断面速度分布,以及射流对液体熔池的穿透深度和冲击面积等一些规律性的结果。根据这些结果建立了数学模型,并结合首钢试验厂5吨转炉熔炼时间的研究,相对地放大到实际生产炉上去,进行了381炉热模拟试验。结果证明,在不影响冶炼效果的条件下,平均每炉吹氧时间由14分钟缩短到12分钟是可行的。     

氧枪喷头在使用过程中射流特性的变化及其对冶炼的影响

本文通过对新旧喷头(包括3孔铸造和3孔锻造喷头)的冷态测定和转炉吹炼结果比较。研究了氧枪喷头在使用过程中射流特性的变化及其对冶炼的影响。比较新旧喷头的射流特性可知,旧喷头的流量减少2％～4％左右,其诸股射流掺混显著,并伴随着射流中心速度的降低,对于严重破损的锻造喷头,诸股射流汇成一股后,流股衰减变得缓慢,有可能会导致过大的穿透深度而影响炉底寿命。比较新旧喷头的吹炼结果可知,旧喷头具有显著的化渣不良,脱磷与脱硫效果较差、终渣(FeO)高,以及锰烧损量大等不良现象。根据上述实验结果,对喷头的更换标准提出了建议。     

Mathematical Modeling of VOD Oxygen Nozzle Jets

This study has focused on numerically exploring the oxygen flow in the convergent‐divergent De Laval nozzle. The De Laval nozzle has been commonly used as oxygen outlet at the lance tip in the vacuum oxygen decarburization (VOD) process. The nozzle geometry used in an active VOD plant was investigated by isentropic nozzle theory as well as by numerical modeling. Since an optimal nozzle design is only valid for a certain ambient pressure, one VOD nozzle will be less efficient for a large part of the pressure cycle. Different ambient pressures were used in the calculations that were based on the De Laval nozzle theory. Flow patterns of the oxygen jet under different ambient pressures were studied and the flow information at different positions from the nozzle was analyzed. In addition, the study compared the effects of different ambient temperatures on jet velocity and dynamic pressure. The predictions revealed that the modeling results obtained with the CFD modeling showed incorrect flow expansion, which agreed well with the results from the De Laval theory. Moreover, a little under‐expansion is somewhat helpful to improve the dynamic pressure. The jet dynamic pressure and its width for the specific nozzle geometry have also been studied. It has been observed that an altering ambient pressure can influence the jet momentum and its width. In addition, a high ambient temperature has a positive effect on the improvement of the jet dynamic pressure.     

Behaviours of supersonic oxygen jet with various Laval nozzle structures in steelmaking process

The top-blowing supersonic oxygen jet is now used widely in steelmaking and metal refining processes. However, the ambient temperature and oxygen flow rate is changed during top-blowing process, making the flow field of supersonic oxygen jet unstable. Hence, it is very important to research the behaviour of supersonic oxygen jet in high ambient temperature. In the present study, the supersonic coherent jet flow fields with 2 kinds of Laval nozzle structures were analysed at various ambient temperature conditions. The total temperature and axial velocity were measured by experiment to verify simulation results. Based on the results, the design method of characteristic-line equation could be more effective in the control the velocity vector of oxygen jet, compared with the one-dimension isoentropic flow theory. As a result, the Laval nozzle designed by characteristic-line equation could suppress the forming of shock wave, reduce the radial velocity and increase the stirring ability of oxygen jet under various ambient conditions.     

Effect of shrouding Mach number and ambient temperature on the flow field of coherent jet with shrouding Laval nozzle structure

The coherent jet technology was widely used to improve the stirring effect of molten bath in steelmaking field, and the key to this technology was to form a low-density zone around the main oxygen jet by a high-temperature shrouding flame. With this revelation, a shrouding nozzle was processed to a Laval nozzle structure fitted with a loop arrangement for increasing the velocity of shrouding jet. For further increasing the area of the low-density zone, the preheating method was also adopted in this new coherent lance structure. In this paper, the effect of Mach number of the shrouding nozzle on the flow field of the coherent jet was investigated at room and high ambient temperature using numerical simulation and experimental studies. The result represented the simulation model used in this research showed good agreement with the experimental data at the texted conditions. Although the shock wave formed by the shrouding jet removed more kinetic energy form the main oxygen jet, the impaction ability of the coherent jet was much bigger than that of conventional supersonic jet, and this phenomenon would be further strengthen if ambient temperature and Mach number of the shrouding nozzle increases.     

Computational Fluid Dynamics Simulation of Supersonic Oxygen Jet Behavior at Steelmaking Temperature

Supersonic oxygen jets are used in steelmaking and other different metal refining processes, and therefore, the behavior of supersonic jets inside a high temperature field is important for understanding these processes. In this study, a computational fluid dynamics (CFD) model was developed to investigate the effect of a high ambient temperature field on supersonic oxygen jet behavior. The results were compared with available experimental data by Sumi et al. and with a jet model proposed by Ito and Muchi. At high ambient temperatures, the density of the ambient fluid is low. Therefore, the mass addition to the jet from the surrounding medium is low, which reduces the growth rate of the turbulent mixing region. As a result, the velocity decreases more slowly, and the potential core length of the jet increases at high ambient temperatures. But CFD simulation of the supersonic jet using the k−ε turbulence model, including compressibility terms, was found to underpredict the potential flow core length at higher ambient temperatures. A modified k-ε turbulence model is presented that modifies the turbulent viscosity in order to reduce the growth rate of turbulent mixing at high ambient temperatures. The results obtained by using the modified turbulence model were found to be in good agreement with the experimental data. The CFD simulation showed that the potential flow core length at steelmaking temperatures (1800 K) is 2.5 times as long as that at room temperature. The simulation results then were used to investigate the effect of ambient temperature on the droplet generation rate using a dimensionless blowing number.     

中厚板控冷及淬火冷却形式选用分析

 目前对常压柱状流及中高压射流的冷却能力一般仅停留在定性认识基础上,而没有从量上揭示这两种喷流形式冷却能力。利用ANSYS对中厚板控冷及淬火中常压柱状流及中高压喷射流冷却的钢板温度场进行了实验及数值模拟,研究两种不同形式的喷流在实际冷却中温降速率大小,研究两种喷流的最大冷却能力,得到两种喷流在实际装置中最大淬火钢板厚度,从而为控冷及淬火装置的选型及设计提供理论依据。