The no-slip boundary condition in fluid mechanics

Ideas leading to the resolution of the problem of no-slip condition for fluid velocity at a solid surface are traced in this concluding part of the article. In the continuum limit velocity slip being zero is established beyond any doubt now. Even turbulent flows which have a large velocity gradient near a wall have to satisfy the no-slip condition at every instant. From molecular considerations, on the other hand, we know that the velocity slip is proportional to the mean free path which may not be negligible in rarefied gas flows. Experimental verification of no-slip has been only indirect and it is only recently that slip velocity in non-wettable liquids has been measured directly.     

The no-slip boundary condition in fluid mechanics

A moving fluid in contact with a solid body cannot have velocity relative to the body. Even though the question whether there is slip has been satisfactorily resolved now, it was a difficult and controversial problem. In the first part of this article several basic ideas and details related to this problem are discussed. The concluding part of the article will trace the development of ideas leading to the resolution of this important question. Extreme cases where fluid does slip will also be discussed.     

The challenge of fluid flow

You look up at the sky, and see a lovely cloud; you look down, and may see lovely ripples on a rivulet (or river). On a hot summer afternoon you see dancing dust devils; on a cold winter evening you can see smoke rising lazily from achulah, and hang up there as if it has given up. You peer at a telescope, and see intense supersonic jets, or vast whirling galaxies; you measure in a wind tunnel, and sense powerful tornadoes behind an aircraft wing. The universe is full of fluid that flows in crazy, beautiful or fearsome ways. In our machines and in the lab, as in terrestrial nature, one sees this amazing diversity in the flow of such a simple liquid like water or a simple gas like air. What is it that makes fluid flows so rich, so complex-some times so highly ordered that their patterns can adorn a saree border, sometimes so chaotic as to defy analysis? Do thesame laws governall that extraordinary variety? We begin with a picture gallery of a number of visible or visualized flows, and consider which ones we understand and which ones we do not, which ones we can compute and which ones we cannot; and it will be argued that behind those all-too-common but lovely flows lie deep problems in physics and mathematics that still remain mysteries.     

多功能流体流动实验装置

在对流体流动阻力及离心泵特性曲线和管路特性曲线测定的基本原理分析研究基础上,自主设计并制作了多功能流体流动实验装置。该实验装置既可进行层流和湍流流型下流体流动阻力的测定,还可以进行不同转速下的离心泵特性曲线和管路特性曲线的测定,从而一方面使设备的制作、维护成本和实验用房面积大大降低,另一方面学生的受训效率大大增加。     

矩形管道内充分发展热流动的可视化计算

推导了求解矩形管道内充分发展流体流动和热交换的有限差分方程,编写了相应的计算机程序,借此求得了管道横截面内速度和温度的结点值,然后利用计算机图形显示算法自动生成相应的速度和温度等值线图形．最后,对管道内充分发展热流动的特性进行了讨论．     

具有水平流动的混合流体对流的扰动方程组

讨论了混合流体对流的流体力学方程组和扰动方程组。基于布辛涅斯克近似,给出了考虑Soret效应和Dufour效应的混合流体对流的基本方程组,对其进行了无因次化处理。给出了基本方程组的无对流运动的传导解。对于混合液体在忽略Dufour效应的情况下,引入扰动物理量,推导了具有水平流动的混合流体对流的扰动方程组。应用扰动方程组可以计算具有水平流动的混合流体对流的稳定性和对流特性。根据不同的简化条件,具有水平流动的混合流体对流的扰动方程组可以变成具有水平流动的单流体对流情况,混合流体对流情况,单流体对流情况,或者单流体水平流动情况的扰动方程组等。如果忽略扰动方程组中二阶以上的高阶项,方程组可简化成线性稳定分析的扰动方程组。     

Iterative method on well bore boundary in numerical modeling of variably saturated flow

An iterative method was developed for incorporating the well bore boundary into the finite difference model of water flow in variably saturated porous media. Six cases were presented involving groundwater pumping or injection to demonstrate the advantages of the iterative method over the traditional method. For the iterative method, the total flux gradually approached the well discharge and the flux profile was non-uniform. And the iterative method took into account the variation of well bore water table. Compared to the traditional method, the iterative method can simulate the variably saturated flow caused by pumping or injection more realistically.     

Infants' sensitivity to boundary flow information for depth at an edge

We investigated infants' sensitivity to a recently discovered kinetic depth cue, boundary flow. 5-month-old infants viewed computer-generated displays in which the relation between the motion of a boundary, indicating an edge, and 2 regions of dots on either side of the boundary, indicating surfaces, provided the only information specifying the order of the 2 surfaces in depth. Infants showed a significant reaching preference for the apparently nearer region of the display. Since previous research has demonstrated that infants reach more frequently for the nearer of 2 surfaces, this result indicates that 5-month-old infants are sensitive to boundary flow information for depth at an edge.     

阿炳与贝多芬创作风格之比较

同为音乐巨匠 ,阿炳和贝多芬为人类留下了永恒的音乐 ,他们的身世极为相似 ,然而创作风格却迥然不同     

On the hydrodynamic stability of a particle-laden flow in growing flat plate boundary layer

INTRODUCTION Turbulent particulate flows occur in many in-dustrial applications, such as in pneumatic transportof particulates, cyclone separators and chemical re-actors. The particles suspended in fluid play a role inthe turbulence modulation, which has been known forseveral years. The observation that adding dust to airflowing in turbulent motion through a pipe can ap-preciably reduce the resistance coefficient was re-ported by Sproull (1961). The observation can beexpressed as saying …     

3D couette flow of dusty fluid with transpiration cooling

INTRODUCTION Transpiration cooling is a very effective process to protect certain structural elements like combustion chamber walls, exhaust nozzles, or gas turbine blades in turbojet and rocket engines, from the influence of hot gases. In view of this, Eckert (1958) obtained an exact solution of the plane couette flow with transpi-ration cooling. The problem remained 2D due to the uniform injection and suction applied at the porous plates. Flow and heat transfer along a plane wall with…     

开放边界条件下的无控制三岔路交通流的研究

文章以改进的NS模型为基础,建立了无控制三岔路模型,通过数值模拟,研究了在开放边界条件下,安全距离,刹车概率共同作用时交通流所呈现的特点。     

A general boundary solution method for potential flow around a 2D semi-infinite body

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板翅换热器入口位置不同翅片排列方式对流体流动与换热的影响

目的：研究板翅换热器入口位置（入口段、导流段以及换热段）在不同翅片排列方式下,换热器流道内流体流动以及温度变化情况,期望得到能够实现
　　最优传热效果的板翅换热器入口位置合理的翅片排列方式。方法：1.构建7种不同入口翅片排列（入口段：导流段：换热段分别为5：8：11,5：8：6,5：8：21,5：4：11,5：16：11,9：8：11和3：8：11）,研究不同翅片排列下换热器入口位置流场以及温度场变化。2.分析板翅换热器入口位置6种不同网格划分结果（网格数分别为11962,39344,2120,207998,90738和54496）对计算误差的影响,验证网格收敛性。结论：通过分析板翅换热器入口位置不同翅片排列方式下换热器入口位置流场与温度场变化可以看出,相比入口段与换热段,导流段翅片排列对换热器温度场影响较大。强化导流段翅片排列可以使换热器获得更好的传热效果。     

Computational fluid dynamics simulation of the wind flow over an airport terminal building

Turbulence in the wake generated by wind flow over buildings or obstacles may produce complex flow patterns in downstream areas. Examples include the recirculating flow and wind deficit areas behind an airport terminal building and their potential impacts on the aircraft landing on nearby runways. A computational fluid dynamics （CFD） simulation of the wind flow over an airport terminal building was performed in this study of the effect of the building wake on landing aircraft. Under normal meteorological conditions, the studied airport terminal building causes limited effects on landing aircraft because most of the aircraft have already landed before entering the turbulent wake region. By simulating the approach of a tropical cyclone, additional CFD sensitivity tests were performed to study the impacts of building wake under extreme meteorological conditions. It was found that, in a narrow range of prevalent wind directions with wind speeds larger than a certain threshold value, a substantial drop in wind speed （〉3.6 m/s） along the glide path of aircraft was observed in the building wake. Our CFD results also showed that under the most critical situation, a drop in wind speed as large as 6.4 m/s occurred right at the touchdown point of landing aircraft on the runway, an effect which may have a significant impact on aircraft operations. This study indicated that a comprehensive analysis of the potential impacts of building wake on aircraft operations should be carried out for airport terminals and associated buildings in airfields to ensure safe aviation operation under all meteorological conditions and to facilitate implementation of precautionary measures.     

Existence and uniqueness theorem for flow and heat transfer of a non-Newtonian fluid over a stretching sheet

Analysis is carried out to study the existence, uniqueness and behavior of exact solutions of the fourth order nonlinear coupled ordinary differential equations arising in the flow and heat transfer of a viscoelastic, electrically conducting fluid past a continuously stretching sheet. The ranges of the parametric values are obtained for which the system has a unique pair of solutions, a double pair of solutions and infinitely many solutions.     

微分求积法求解不可压二阶粘弹性流体和热迁移模型中的稳态流动

1IntroductionAlthoughthe computation of the fluid mechanics hasgreat development during the last decades,due to themodel in nonlinear fluid mechanics is very complicat-ed,the more efficient techniques for solvingthis prob-lemstill attract the interest of many researchers.Thedifferential quadrature method(DQM)introduced byBell man,et al.[1,2]is an efficient numerical methodfor solving partial differential equations.In recentyears,the DQMhas been widely used for solving theproblems of enginee…