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1、1. Fluid motion can usually be described by one of several simplified modes of action or models.流体的运动通常可以用几个简化的模型之一加以描述2. The simplest is the ideal-fluid model, which assumes no resistance to shearing.最简化的就是理想流体模型，它假设对切应力没有阻力3. Ideal flow analysis is well developed, and when properly interpreted is
2、valid for a wide range of applications.理想流体得到了很好的发展，当加以很好的解释和界定，在很大的应用范围内是有效的4. Most fluids in HVAC applications can be treated as Newtonian, where the rate of deformation is directly proportional to the shearing stress.暖通空调所应用的流体可以被看作牛顿流体，变形率与切应力成正比5. Viscosity is the resistance of adjacent fluid l
3、ayers to shear. For shearing between two parallel plates, each of area A separated by distance Y, the tangential force F per unit area required to slide one plate with velocity V parallel to the other is proportional to V/Y.黏度是相邻的流体层对切应力的阻力，对于两块平行平板之间的切力来说，它们的面积为A，间距为Y，单位面积上的切线拉力F要想让一块平板以速度v与另一块平板平行
4、滑动6. For gases (except near the critical point), viscosity increases with the square root of the absolute temperature, as predicted by kinetic theory. Liquid viscosity decreases with increasing temperature.对于气体，除近临界之外，黏度随着绝对温度的平方根的增加而增大的，正如动量定理所预测的那样7. Pressure variation in fluid flow is important a
5、nd can be easily measured. Variation across streamlines involves fluid rotation (vorticity). 压力的变化在流体流动中是很重要的,可以很容易的测量。流线横向变化涉及到流体旋转（涡流）8. This relation explains the pressure difference found between the inside and outside walls of a bend and near other regions of conduit section change. It also sta
6、tes that pressure variation is hydrostatic across any conduit where streamlines are parallel.这个关系式就解释了一个弯头内外壁之间以及在靠近管道截面区域变化的一种压力差。在流线相互平行的管道截面上的压力变化是呈流体静力学分布的9. The first law of thermodynamics can be applied to mechanical flow energies (kinetic and potential) and thermal energies: heat is a form of
7、 energy and energy is conserved. 热力学第一定律可应用于机械流能量(动能和势能)和热量:热是能量的一种形式，能量是守恒的。10. Fluid energy is composed to kinetic, potential (due to elevation z), and internal (u) energies.流体的能量是由动能、势能以及内能所组成的11. Identical results are obtained with the three forms if the units are consistent and the fluids are h
8、omogeneous.如果方程两边各项单位是统一而且均质的，用三种形式可以得到完全相同的结果12. Two- and three-dimensional details of local flow occurrences are still significant, but their effect is combined and accounted for in factors.尽管在局部二维的或三维的流动仍然很明显，但他们的影响可以被综合起来用系数表示13. In fluid flow past fixed boundaries, the velocity at the boundary
9、is zero and shear stresses are produced. The equations of motion then become complex and exact solutions are difficult to find, except in simple cases. 在流体流过固定边界，靠近边界的速度为0，产生切应力。运动方程变得复杂了，很难找到精确解，除了简单的例子14. The parabolic velocity profile can also be derived for the axisymmetric conduit (pipe) of rad
10、ius R but with a different constant.对于半径为R轴对称管道来说，也可以得出抛物线型规律15. Fluid flows are generally turbulent, involving random perturbations or fluctuations of the flow (velocity and pressure), characterized by an extensive hierarchy of scales or frequencies.流体的流动很多都有湍流，涉及流动的随机扰动或者流体的波动（速度和压力），其特征是在很大程度上有不同
11、的频率16. Flow disturbances that are not random, but have some degree of periodicity, such as the oscillating vortex trail behind bodies, have been erroneously identified as turbulence.流动扰动不是随机的，具有一定的周期性，比如流体后面震荡的涡流轨迹，被错误的认为17. Only flows involving random perturbations without any order or periodicity
12、are turbulent; the velocity in such a flow varies with time or locale of measurement.只有包含了随机扰动，这种扰动没有规律和周期可寻就是湍流；这样的流动中的速度随着测量地点不同发生变化18. Turbulence can be quantified by statistical factors.Thus, the velocity most often used in velocity profiles is the temporal average velocity v, and the strength o
13、f the turbulence is characterized by the root-mean-square of the instantaneous variation in velocity about this mean.紊流能被量化的统计出来。所以，速度常用时均流速，湍流的强度具有速度与时均速度的差值的平方根的大小来量度19. Sometimes in turbulent flow studies, velocity at the wall may appear finite implying a fluid slip at the wall. 有时在湍流研究中，这意味着在流体滑
14、动墙上，壁面速度可能出现无穷大的量20. Zero wall velocity leads to a high shear stress near the wall boundary and a slowing down of adjacent fluid layers.0壁面的速度导致了在靠近边壁的边界处有较高的切应力从而使相邻流体层的速度变慢21. A velocity profile develops near a wall, with the velocity increasing from zero at the wall to an exterior value within a
15、finite lateral distance.靠近壁面的边界速度分布规律，在由壁面处的0值快速增加到来流速度或边界来流速度22. Turbulent flow profiles are flat compared to the more pointed profiles of laminar flow. Near the wall, velocities of the turbulent profile must drop to zero more rapidly than those of the laminar profile, so the shear stress and frict
16、ion are much greater in the turbulent flow case.与层流的速度分布扁平相比，湍流更尖锐一些，壁面处湍流的速度要比层流的速度更快地降为0，因此在湍流的情况下，切应力与摩擦力更大一些23. In most flows, the friction of a bounding wall on the fluid flow is evidenced by a boundary layer. For flow around bodies, this layer (which is quite thin relative to distances in the flow direction) encompasses all viscous or turbulent actions, causing the velocity i
