热能与动力工程专业英语翻译李瑞扬.docx

1、热能与动力工程专业英语翻译李瑞扬热能与动力工程专业英语-翻译(李瑞扬)1.3 The Characteristics of Fluids 流体的特征constituent：组成的；tangential：切向的；restrain：限制、约束；equilibrium：平衡， 均衡；interface：相互关系、分界面；molecule：微小颗粒、分子；continuum：连续体； vessel：容器；tar：焦油、柏油；pitch：树脂；imperceptibly：察觉不到的，细微的； restore：恢复；subside：下沉、沉淀、减退、衰减；hypothetically：假设地、假想地； s

2、phere：球、球体；microvolume：微元体积；rarest：最稀罕的，虽珍贵的A fluid is a substance which may flow; that is, its constituent particles may continuously change their positions relative to one another. Moreover, it offers no lasting resistance to the displacement, however great, of one layer over another. This means t

3、hat, if the fluid is at rest, no shear force (that is a force tangential to the surface on which it acts )can exist in it. A solid, on the other hand, can resist a shear force while at rest; the shear force may cause some displacement of one layer over another, but the material does not continue to

4、move indefinitely. In a fluid, however, shear forces are possible only while relative movement between layers is actually taking place. A fluid is further distinguished from a solid in that a given amount of it owes its shape at any particular time to that of a vessel containing it, or to forces whi

5、ch in some way restrain its movement. 流体是可以流动的物质，也就是说，组成流体的质点可以连续的改变它们的相对位置。而且，不管层与层之间的相对位移有多大都不会产生持久的抵抗力。这意味着流体在静止状态下是不会存在剪切力的（剪切力是与其作用表面相切的力）。另一方面，固体在静止时却可以抵抗剪切力，其中的剪切力也可以使层与层之间发生相对位移，但是固体材料却不一定会有连续的运动。然而在流体中，只有当层与层之间有相对运动产生时才会有剪切力存在。流体和固体的进一步区别还在于在特定的时刻，确定数量的流体其形状取决于承载它的容器，或者取决于一些限制其运动的力。 The dis

6、tinction between solids and fluids is usually clear, but there are some substances not easily classified. Some fluids, for example, do not flow easily: thick tar or pitch may at times appear to behave like a solid. A block of such a substance may be placed on the ground, but, although its flow would

7、 take place very slowly, yet over a period of time-perhaps several days-it would spread over the ground by the action of gravity, that is, its constituent particles would change their relative positions. On the other hand, certain solids may be made to flow when a sufficiently large force is applied

8、; these are known as plastic solids. 固体和流体之间的区别通常是很明显的，但是也有些物质难于归类。比如说有些流体并不易流动，如重油和树脂有时候会表现得像固体一样，像这样的一块物质如果放在地面上，虽然它的流动发生的非常缓慢，要经过很长的一段时间也许要好几天，但是在重力的作用下它仍然会在地面上蔓延开来，也就是说，它的组成质点会改变它们之间的相对位置。另一方面，某些固体当足够大的力作用时也会“流动”，这就是我们所知的“塑性固体”。Even so, the essential difference between solids and fluids remains.

9、 Any fluid, no matter how thick or viscous it is, begins to flow, even if imperceptibly, under the action of the slightest net shear force. Moreover, a fluid continues to flow as long as such a force is applied. A solid, however, no matter how plastic it is, does not flow unless the net shear force

10、on it exceeds a certain value. For forces less than this value the layers of the solid move over one another only by a certain amount. The more the layers are displaced from their original relative positions, however, the greater are the forces resisting the displacement. Thus, if a steady force is

11、applied, a state will be reached in which the force resisting the movement of one layer over another balance the force applied and so no further movement of this kind can occur. If the applied force is then removed, the resisting forced will tend to restore the solid body to its original shape.即便如此，

12、固体和流体之间依然有本质的差异。任何流体，无论多“稠”或者粘性多大，在最微小的剪切力作用下都会流动，即便这种流动是极其细微的。而且，只要这种力持续作用，流体就会连续流动。然而对于固体，不管它的可塑性有多强，只有当作用其上的净剪切力超过一定数值后才会流动，而小于该值的力所引起的固体层之间的相对移动是有限的。层偏离原始位置的程度越大，抵抗这种变形的力也就越大。因此，当一恒定力作用时，就会达到这样一个状态：即会产生一个抵抗这种层间相对运动的力以平衡所施加的外力，所以不会产生进一步的运动。如果将所施加的外力移除，抵抗力将会使固体恢复到它的原始形状。In a fluid, however, the fo

13、rces opposing the movement of one layer over another exist only while the movement is taking place, and so static equilibrium between applied force and resistance to shear never occurs. Deformation of the fluid takes place continuously so long as a shear force is applied. But if this applied force i

14、s removed the shearing movement subsides and, as there are then no forces tending to return the particles of fluid to their original relative positions, the fluid keeps its new shape. 然而，在流体中，只有当层间相对运动发生时才会存在这种阻止运动的力。所以不会存在这种外力和抵抗力之间的静态平衡。只要有剪切力作用，流体便会产生连续变形。但是如果将外力移除，剪切运动便会减退，而且因为这时没有使流体质点回到它们初始位置的

15、力，所以流体将保持它的“新”形状。Fluids may be sub-divided into liquids and gases. A fixed amount of a liquid has a definite volume which varies only slightly with temperature and pressure. If the capacity of the containing vessel is greater than this definite volume, the liquid occupies only part of the container,

16、 and it forms an interface separating if from its own vapour, the atmosphere or any other gas present. 流体可以划分为液体和气体。一定数量的液体其所占据的体积也是一定的，它随温度和压力的变化很小。如果容器的体积大于这个一定的体积，那么液体占据的只是容器的一部分，而且会形成一个分界面将液体与该液体的蒸汽、空气或其它存在的气体分开。On the other hand, a fixed amount of a gas, by itself in a container, will always ex

17、pand until its volume equals that of the container. Only then can it be in equilibrium. In the analysis of the behaviour of fluids the most important difference between liquids and gases is that, whereas under ordinary conditions liquids are so difficult to compress that they may for most purposes b

18、e regarded as incompressible, gases may be compressed much more readily. Where conditions are such that an amount of gas undergoes a negligible change of volume, its behaviour is similar to that of a liquid and it may then be regarded as incompressible. If, however, the change in volume is not negli

19、gible, the compressibility of the gas must be taken into account in examining its behaviour.而另一方面，容器内一定数量的气体则通常都要膨胀到和容器相等的体积。这样它才会达到平衡状态。在分析流体特性时，液体和气体之间最重要的差异在于：鉴于在通常的条件下液体是难以压缩的，因此常常将液体认为是不可压缩流体，而气体则容易压缩的多。当一定量的气体其体积变化可以被忽略的情况下，气体的表现和液体类似，因此也可以认为是不可压缩的。然而，如果体积的变化不可忽略，那么在分析其行为特征时就必须考虑气体的压缩性。In cons

20、idering the action of forces on fluids, one can either account for the behavior of each and every molecule of fluid in a given field of flow or simplify the problem by considering the average effects of the molecules in a given volume. In most problems in fluid dynamics the latter approach is possib

21、le, which means that the fluid can be regarded as a continuum-that is, a hypothetically continuous substance. 在考虑作用于流体上的力时，可以用给定流动区域内的流体上每个分子的行为来解释，也可以只考虑给定体积内分子的平均效应而使问题得以简化。在流体动力学的许多问题中后一种方法是可行的，这意味着将流体看作是连续介质即一种假想的连续介质。The justification for treating a fluid as a continuum depends on the physical

22、dimensions of the body immersed in the fluid and on the number of molecules in a given volume. Let us say that we are studying the flow of air past a sphere with a diameter of 1 cm. A continuum is said to prevail if the number of molecules in a volume much smaller than the spheres is sufficiently gr

23、eat so that the average effects ( pressure, density, and so on ) within the volume either are constant or change smoothly with time. 是否可以将流体看作是连续介质取决于浸入流体的物体的尺寸和给定体积内的分子数目。比如我们现在研究空气流过一个直径为1厘米的球体的问题。如果在比球的体积小得多的体积内流体分子数目足够多以至于该体积的平均效应（压力、密度等等）为常数或者随时间缓慢变化，就认为该流体是连续介质。The number of molecules in a cub

24、ic meter of air at room temperature and sea-level pressure is about 1025. Thus the number of molecules in a volume of 10-19 m3 (about the size of a dust particle, which is very much smaller than the sphere) would be 106 . This number of molecules is so large that the average effects within the micro

25、volume are indeed virtually constant. On the other hand, if the 1 cm sphere were at an altitude of 305 km, there would be only one chance in 108 of finding a molecule in the microvolume, and the concept of an average condition would be meaningless. In this case, the continuum assumption would not be

26、 valid for fluid flow except in the rarest conditions, such as those encountered in outer space. 在室温、海平面压力下，每平方米空气中的分子数大约为1025个，因此10-19 m3体积中的分子数为106个（10-19 m3大约是一个灰尘的体积，这要远远小于上面所说的球体）。如此多的分子数目使得在该微元体积内的平均效应实际上为常数。另一方面，如果1厘米的球体被置于海拔305千米处，那么在该微元体积内发现一个分子的概率只有108分之一，所以平均状态的概念也就没有任何意义。在这种情况下，除了像在外层空间这

27、种空气非常稀薄的情况之外，流体流动的连续性假设都是无效的。1.4 Scope Significance and Trend of Fluid MechanicsFluid mechanics,as the name indicates,is that branch of applied mechanics which is concerned with the statics and dynamics of liquids and gases.Dynamics,the study of motion of matter,may be divided into two part-dynamics

28、 of rigid bodies and dynamics of non-rigid bodies. The latter is usually further divided into two general classifications-elasticity(solid elastic body) and fluid mechanics.流体力学，正如名字所指，是和液体，气体的静态和动态有关的应用力学的分支。动力学，物体运动的研究，可以分为两部分刚性物体动力学和无刚性物体动力学。后者通常进一步分为两大一般类别。弹性（固定弹性物体）和流动力学。The subject of fluid me

29、chanics can be subdivided into two broad categories: hydrodynamics and gas dynamics. Hydrodynamics deals primarily with the flow of fluids for which there is virtually no density change,such as liquid flow or the flow of gas at low speeds.Hydraulics,for example, the study of liquid flows in pipes or

30、 open channels, falls within this category. The study of fluid forces on bodies immersed in flowing liquids or in low-speed gas flows can also be classified as hydrodynamics.流体力学学科可以再分为两大广泛的类别：水动力学和气体动力学。水动力学主要处理的是实际没有密度变化的流体流动。例如液体和气体在低速情况下的流动。水动力学，例如在管道和开放式通道中液体流动的研究，属于这一类别。对浸入流动液体和低速流动其他的物体所受流体力的

31、研究也可以分类为水动力学。Gas dynamics,on the other hand, deals with fluids that undergo significant density changes.High-speed gas flowing through a nozzle or over a body ,the flow of chemically reacting gases, or the movement of a body through the low density air of the upper atmosphere falls within the genera

32、l category of gas dynamics.气体动力学，另一方面，处理经历有效密度变化的流体。高速气体流动通过一个喷嘴或者掠过一个物体，发生化学反应气体的流动，物体通过更高大气中低密度空气中的运动属于气体动力学的一般类别。An area of fluid mechanics not classified as either hydrodynamics or gas dynamics is aerodynamics, which deals with the flow of air past aircraft or rockets,whether it be low-speed inc

33、ompressible flow or high-speed compressible flow.流体力学中即不归类水动力学也不属于气体动力学的那一领域称为航空动力学，它处理穿过飞机和火箭的空气流动，是否它是低速不可压缩流动或者是高速可压缩流动。There are, however,two major aspects of fluid mechanics which differ from solid-body mechanics.The first is the nature and properties of the fluid itself, which are very different from those