文档介绍：完全气体
内能和焓
热力学复习热力学第一定律
熵及热力学第二定律
等熵关系式
压缩性定义
无粘可压缩流动的控制方程
总条件的定义
有激波的超音速流动的定性了解
第七章路线图
. DEFINITION PRESSIBILITY
(压缩性定义)
All real substances pressible to some greater or lesser extend. When you squeeze or press on them, their density will change. This is particularly true of gases.
(所有的真实物质都是可压缩的,当我们压挤它们时,它们的密度会发生变化,对于气体尤其是这样.)
The amount by which a substance can pressed is given by a specific property of the substance called pressibilty , defined below.
物质可被压缩的大小程度称为物质的压缩性.
Consider a small element of fluid of volume .
The pressure exerted on the sides of the element is p. If the pressure is increased by an infinitesimal amount dp, the volume will change by a negative amount .
By definition, pressibility is given by:
()
as
()
Physically, pressibility is a fractional change in volume of the fluid element per unit change in pressure.(从物理上讲,压缩性就是每单位压强变化引起的流体微元单位体积内的体积变化)
If the temperature of the fluid element is held constant, then is identified as the pressibility (等温压缩性)
()
If the process takes place isentropically, then (等熵压缩性)
()
If the fluid is a gas, pressibility is large, then for a given pressure change from one point to another in the flow , Eq.() states that can be large. (如果流体为气体,则值大,对于一个给定压强变化,方程.()指出, 也会大.)
Thus, is not constant; the flow of a gas is pressible flow.
The exception is the low-speed flow of a gas. Where is the limit? If the Mach number
, the flow should be pressible.
()
GOVERNING EQUATIONS FOR INVISCID, COMPRESSIBLE FLOW (无粘、可压缩流控制方程)
For inviscid, pressible flow, the primary dependent variables are the pressure p and the velocity . Hence, we need only two basic equations, namely the continuity and the momentum equations.

对于无粘、不可压缩流动,基本自变量是压强 p和速度。因此我们只需要两个基本方程,即连续方程和动量方程。
Indeed, the basic equations bined to obtain Laplace’s equation and Bernoulli’s equation, which are the primarily tools the applications discussed in Chaps. 3 to 6. Note that both and T are assume