Analyses and Modeling of Laminar Flow in Pipes Using Numerical Approach

This paper investigate some important works done on numerical analysis and modeling of laminar flow in pipes. This review is focused on some methods of approach and the analytical tools used in analyzing of the important parameters to be considered in laminar flow;such as frictional losses, heat transfer etc. in laminar flow in pipes of different shapes, and the importance of laminar flow in its areas of applications. Prominent researchers have approached this from different perspectives. Some carried out analysis on the pressure drop as a function of permeability, some worked on friction factor analysis, some discussed heat transfer effects of laminar flow in the entrance region, while some discussed its applications in various industries. Some of these works were done considering a given form of pipe configuration or shape which is circular pipes. Only a few, of the literature reviewed have related their considerations to different forms of pipes. Most consider pipes to be majorly circular in shape, but in industries today some circular pipes have become elliptical in shape due to long time usage of the pipes, which would have contributed to increase in some different forms of losses in the industries. In engineering, efficiency and effectiveness improvement is the major goal, if a research work has been done, considering the important parameters in laminar flow showing their effects on different forms of pipe configuration as a result of pipe deformation due to usage, huge amount of money will be saved. This will show clearly how the efficiency of a given circular pipe has seriously been affected due to deformation, and the level of loss this has resulted to.

Robust design of natural laminar flow supercritical airfoil by multi-objective evolution method

Abstract A transonic, high Reynolds number natural laminar flow airfoil is designed and studied. The γ-θ transition model is combined with the shear stress transport （SST） k-w turbulence model to predict the transition region for a laminar-turbulent boundary layer. The non-uniform free-form deformation （NFFD） method based on the non-uniform rational B-spline （NURBS） basis function is introduced to the airfoil parameterization. The non-dominated sorting genetic algorithm-II （NSGA-II） is used as the search algo- rithm, and the surrogate model based on the Kriging models is introduced to improve the efficiency of the optimization system. The optimization system is set up based on the above technologies, and the robust design about the uncertainty of the Mach number is carried out for NASA0412 airfoil. The optimized airfoil is analyzed and compared with the original airfoil. The results show that natural laminar flow can be achieved on a supercritical airfoil to improve the aerodynamic characteristic of airfoils.

NUMERICAL STUDY ON EFFECT OF OPERATING TABLE PROTECTED BY HORIZONTAL LAMINAR FLOW SCREEN

Transmission of airborne bacteria is the main factor causing surgical site infection(SSI),which is harmful to patients′health and even lives.Numerical study is conducted on the effect of the operating table protected by horizontal laminar flow screen.Discrete phase model(DPM)is used.Numerical simulation is carried out to evaluate particle trajectories with the Lagrange approach.As a result,the protecting effect of horizontal laminar flow screen is established,and the protecting parameters of the air velocity supplied by the screen and the protecting distance are optimized.The optimized air velocity supplied by the screen should be at 0.4—0.6 m/s.And the protecting distance should be less than 1.3 m.This work provides references for the study on the depuration of operating table or room.

Experimental Research and Mathematical Model of Drag Torque in Single-plate Wet Clutch

Reduction of drag torque is one of important potentials to improve transmission efficiency.Existing mathematical model of drag torque was not accurate to predict the decrease after oil film shrinking because of the difficulty in modeling the flow pattern between two plates.Flow pattern was considered as laminar flow and full oil film in the gap between two plates in traditional model.Subsequent equivalent circumferential degree model presented an improvement in oil film shrinking due to centrifugal force,but was also based on full oil film in the gap,which resulted difference between model prediction and experimental data.The objective of this paper is to develop an accurate mathematical model for the above problem by using experimental verification.An experimental apparatus was set up to test drag torque of disengaged wet clutch consisting of single friction and separate plate.A high speed camera was used to record the flow pattern through transparent quartz disk plate.The visualization of flow pattern in the clearance was investigated to evaluate the characteristics of oil film shrinking.Visual test results reveal that the oil film begins to shrink from outer radius to inner radius at the stationary plate and only flows along the rotating plate after shrinking.Meanwhile,drag torque decreases sharply due to little contact area between the stationary plate and the oil.A three-dimensional Navier-Stokes （N-S） equation based on laminar flow is presented to model the drag torque.Pressure distributions in radial and circumferential directions as well as speed distributions are deduced.The model analysis reveals that the acceleration of flow in radial direction caused by centrifugal force is the key reason for the shrinking at the constant feeding flow rate.An approach to descript flow pattern was presented on the basis of visual observation.The drag torque predicted by the model agrees well with test data for non-grooved wet clutch.The proposed model enhances the precision for predicting drag torque,and lays down a framework on which some subsequent models are developed.

Modeling and experimental studies of methyl methacrylate polymerization in a tubular reactor

In this study, rheological examination of the mixture of a tubular reactor in which methyl methacrylate was polymerized has been studied. The n(flow behavior index) value of Power Law Model of mixture contained in the reactor has been determined within the span of 0.3492 to 0.9889 by curve fitting. Employing these numerical data for velocity profile, the reactor has been modeled. Moreover, the functions of the reactor have been compared in the three modes of plug, mixed and laminar flow. The results obtained in this research indicate that the polymethyl methacrylate mixture contained in the reactor is pseudo-plastic. Moreover, as the conversion grows, the velocity profile starts as a parabolic profile and approaches the plug mode; although it never reaches the plug. The other conclusions borne in this study indicate that when the reactor's radius is decreased, the conversion rate grows. However, as decreasing the radius would also reduce the productions rate, this procedure is not economical. Finally, in this modeling, the amount of conversion is equal to 56.47% at the end and according to its laboratory proportion which is 55.88%, it has reached the conclusion that the modeling duly undertaken is applicable and valid.

Basic Laws in Mechanics of Turbulent Flows

Turbulent flow is a basic form of fluid motion widely observed in nature. In hydraulic engineering, especially in the study of sediment movement, turbulence is a key problem. In this paper, based on the stochastic theory of wall turbulence developed by the author and the results by other investigators, fluc-tuation and mean structures and drag coefficient for Newtonian and drag reduction flows in all states (laminar, transitional, turbulent) and in all regions (smooth, transitional, rough) are theoretically discussed in detail. General laws for laminar and turbulent flows obtained by the author are verified by the experimental results obtained by others, and there is good agreement between them.

Mathematic modeling on flexible cooling system in hot strip mill

A novel cooling system combining ultra fast cooling rigs with laminar cooling devices was investigated.Based on the different cooling mechanisms,a serial of mathematic models were established to describe the relationship between water flow and spraying pressure and the relationship between water spraying heat flux and layout of nozzles installed on the top and bottom cooling headers.Model parameters were validated by measured data.Heat transfer models including air convection model,heat radiation model and water cooling capacity model were detailedly introduced.In addition,effects on cooling capacity by water temperature and different valve patterns were also presented.Finally,the comparison results from UFC used or not have been provided with respect to temperature evolution and mechanical properties of Q235B steel grade with thickness of 7.8 mm.Since online application of the sophisticated CTC process control system based on these models,run-out table cooling control system has been running stably and reliably to produce resource-saving,low-cost steels with smaller grain size.

两相层流的复阻抗频散模型研究

在油气生产中含水率是进行产能评估和调整开发策略的重要指标,需要寻找一种更为经济有效的含水率检测方法。复阻抗频谱(CIS)检测技术是一种低成本、易实现、环保安全的快速检测方法,具有较大的开发潜力。基于复阻抗频散机理,结合Randles电路和Cole-Cole模型优势提出了一种适用于两相层流的复阻抗频散模型。研究制作了一套两相层流检测装置,并基于频谱分析和粒子群优化算法(PSO)反演获取模型参数,包括等效溶液阻抗、弛豫时间常数、频率相关指数、扩散阻抗系数以及弥散系数,并通过对照实验讨论了含水率和矿化度对模型参数的影响。实验结果表明,新模型计算值与实测值具有较好的一致性,同时模型参数与含水率、矿化度满足幂函数关系,可用于定量评价。该方法在传统测井采用的单频阻抗检测技术基础上修正了地层水矿化度影响,这对生产测井中的产能评估有重要意义。

跨声速自然层流标模CRM-NLF风洞试验快速转捩预测

中国商飞北研中心开发了快速CFD分析工具CFAST进行层流基本流场计算,单工况的计算时间仅为200 s,然后耦合转捩预测模块进行转捩预测分析,大幅缩减了计算周期,从而实现跨声速民机典型后掠机翼三维边界层的快速转捩预测。转捩预测模块基于线性稳定性理论的双e^(N)方法,可以同时考虑横流驻波不稳定模态和Tollmien-Schlichting波不稳定模态对转捩的影响。目前,公开的跨声速高雷诺数民机自然层流试验数据十分稀缺,本文以NASA公开的跨声速高雷诺数自然层流标模CRM-NLF为研究对象,研究了迎角、雷诺数和马赫数对转捩的影响。计算结果与试验结果以及基于RANS的转捩计算结果吻合很好,说明开发的快速转捩预测工具高效可靠,可以用于跨声速民机层流机翼设计和优化。

基于CFD模拟SCC混凝土在溜槽的流动行为

为研究SCC混凝土在溜槽的流速情况,本模拟将分为开口式明渠和封闭式管道研究,初步验证了混凝土明渠流或是管道流的流动特性是一致的,又将混凝土分别以H-B模型、欧拉模型做流动研究,得出在短距离模拟中SCC混凝土是处于层流状态,在长距离流动下,随着砂浆黏滞阻力的减少转为湍流状态,并且由于粗骨料密度大于砂浆密度,会发生一定的沉降。通过增加混凝土屈服应力和塑性黏度,可加强混凝土的流动稳定性。

通道层流场中单颗粒惯性横向迁移的数值研究

为研究通道层流场中单颗粒惯性横向迁移规律,以圆管和方管为例,对层流场中性单颗粒惯性横向迁移现象开展数值模拟研究。将颗粒放在圆管和方管进口截面的若干位置并释放,采用离散颗粒模型,计算粒径d=0.8、1.0、1.2 mm的3种球形颗粒在雷诺数Re=100、125、150条件下,由不同初始位置释放后在流场中的迁移轨迹及横向迁移后所达到的平衡位置。结果表明,对于圆管,颗粒在初始半径分别为0.7R与0.8R(R为圆管半径)处释放时,惯性迁移的平衡位置均在0.6R附近;随着粒径增加,颗粒迁移的平衡位置向管道轴心偏移;随着Re的增加,颗粒迁移的平衡位置向管壁方向偏移。对于方管,颗粒的初始释放位置设定在z0=0.22L与0.33L(L为方管截面边长)处,当颗粒释放位置越靠近通道轴心时,颗粒的横向迁移距离就越短;随着Re的增加,颗粒的平衡位置会更加偏向通道中心;相对于大颗粒,小颗粒的平衡位置更靠近壁面。

方大钢铁3500 mm中厚板不平度攻关实践

分析方大九钢低合金中厚板不平度超标原因,总结了工作辊原始辊形、轧辊磨损和辊系热凸度对不同宽度钢板的板形影响规律。通过建立板形控制参数对应表,动态分配精轧阶段轧制力,控制中间坯两侧厚度差,解决ACC层流冷却及轧机除鳞异常,提高了钢板平直度。

错位六弯叶桨在假塑性流体中的混沌搅拌特性

基于混沌混合理论,提出了一种错位叶片的结构形式,用来消除层流流场的混合隔离区。利用CFD的方法,对六弯叶涡轮(6BT)和错位六弯叶涡轮(6SBT)2种搅拌器在黄原胶水溶液中的流场变化进行研究,分析比较了2种搅拌器的流场结构、速度分布以及功率消耗的不同。结果表明,模拟计算得到的功率值与实验测量值吻合较好,6SBT桨在层流区的临界雷诺数为20;错位叶片搅拌流场结构不对称,可消除流场隔离区,搅动范围变大;随Re增大,对层流流场的改善效果增强,全槽的平均剪切速率得以提高,并且具有节能功效。在转速N=5 r/s的条件下,6SBT桨的轴向和径向速度分布整体上明显好于6BT桨,而功耗约为6BT桨的93%。

模拟沉淀池流速场的层流模型扩展性研究

平流式沉淀池内水流的雷诺数>3 000(为紊流),当利用传统的层流模型进行模拟时不能准确获得沉淀池内的流速场分布,若采用特征涡粘性雷诺数或密布网格,则可以扩展层流模型模拟沉淀池内物理量的适用性。利用混合有限分析解法及交错网格技术对沉淀池内的流动状况进行数值模拟,结果表明沉淀池内存在两个旋涡,在挡板后存在一个较大的回流区,该处的旋涡呈逆时针旋转,另一个旋涡在出口堰底板附近,为顺时针旋转的小旋涡,结果与试验资料吻合良好。

小眼井层流注水泥顶替机理分析

用宾汉流体建立了水泥浆层流顶替钻井液的理论模型。机理分析表明,小眼井中套管偏心对层流注水泥宽窄间隙顶替速度差异影响显著,而顶替压力梯度影响较小。在层流条件下,增加水泥浆动切力和水泥浆与钻井液密度差并减小钻井液动切力,有利于使整个环空钻井液顶替。但由于套管偏心是小眼井环空的显著特征,在实际注水泥中,尽量避免采用层流顶替模式。

板带层流冷却系统仿真软件包的研究与开发

以宝钢2050热连轧的板带层流冷却系统为对象研发了仿真软件包, 对板带轧后在层流冷却控制系统作用下的运行状况进行了全面的仿真。此软件包具有直观、形象、使用快捷、方便的特点,为研究人员研究层流冷却控制系统的设计及产品质量的改进提供了实验的软环境。

层流状态下超疏水表面流场建模与减阻特性仿真研究

在充分发展层流状态下对具有规则微观结构的超疏水表面流场进行数值仿真研究,分析了超疏水表面流场的减阻特性。针对超疏水表面微观结构特点,采用Cassie接触模型,对计算域利用结构化网格进行划分,采用VOF多向流模型进行数值仿真。研究表明:超疏水表面凹槽附近产生压差阻力导致凹槽内部形成低速漩涡,产生推动效应与涡垫效应;超疏水表面减阻率随凹槽槽宽增大而增大,受凹槽深度影响不显著,矩形凹槽比V形凹槽与U形凹槽有更好的减阻效果。

输油管道油流带电的计算模型

给出了层流和紊流条件下新的管道油流带电计算模型。基于Gavis J的放电机理,对管壁-油界面处的边界条件提出了一种新的确定方法。分别推导出了两种流态下简单管道内电荷输运方程的表达式,并对方程的边界条件处理进行了研究。计算模型中考虑了油流速度、油的电导率和油温等因素对油流带电的影响,克服了以往模型中存在着难以确定的变量的缺点。利用计算模型对两条实验油道的油流带电量进行了计算,计算值和实验值的对比结果表明,计算值和实验值比较吻合。

磁绝缘稳态电路编码中等效电感和等效电容的计算

从层流模型出发,根据线电压和线电流,给出了磁绝缘稳态时传输线极间的电磁场分布的解析表达式。在此基础上,计算了考虑空间电子效应后处于磁绝缘稳态的传输线等效分布电感和电容,以改进磁绝缘稳态的电路单元模型。利用该方法,模拟计算了Z加速器的MITL-A在磁绝缘稳态时的等效分布电感和电容。结果表明,等效分布电容随空间电子效应的增强而变大,而等效分布电感随空间电子效应的增强而变小;且线电压越低,等效分布电感和电容随空间电子效应的增强变化越快。

二维翼型抽吸气层流控制技术的数值研究

数值模拟了表面开孔吸气控制下的翼型绕流流场。主要研究了孔径、孔间距、吸气区大小和位置等吸气参数对二维翼型气动性能的影响。计算选用SSTk-ω湍流模型,并对标准的Wilcox转捩模式进行了修正。计算结果表明:修正的转捩模式能较好地模拟表面吸气引起的转捩位置的变化;在不同孔径、孔间距和吸气区位置的吸气控制下,翼型总阻力随吸气系数的增加均呈先减小后增大的变化规律;采用较大的孔径、孔间距以及较小的吸气区域进行吸气控制,具有较大的翼型阻力恢复吸气系数和较低的相对阻力最小值。