能量方程的特殊形式 空气动力学英文教材.pptVIP

正激波基本控制方程的推导;8.4 SPECIAL FORMS OF THE ENERGY EQUATIONS 能量方程的特殊形式 本节需要掌握的内容要点： ? 能量方程的各种特殊表达形式 ? 总温的计算公式 ? 总压、总密度的计算公式 ? 临界参数的定义与计算公式 ? 特征马赫数（速度系数）M*的定义及计算公式 ;? 能量方程的各种特殊表达形式 在7.5节中我们得到了定常、绝热、无粘流动的能量方程：;(8.30);Definition of stagnation speed of sound：驻点音速的定义;(8.38);(8.40);? 总压、总密度的计算公式： 回忆7.5节总压和总密度的定义， 在定义中包含了将气流速度等熵地压缩为零速度。由（7.32）式， 我们有：; Equation (8.40),(8.42)and (8.43) are very important; they should be branded on your mind. They provided formulas from which the defined , and can be calculated from the actual conditions of M ,T ,p and at a given point in general flow field (assuming calorically perfect gas). They are so important that values of and obtained from Eqs. (8.40),(8.42), and (8.43), respectively , are tabulated as functions of M in App.A for (which corresponds to air at standard conditions). 方程(8.40),(8.42)和(8.43) 非常重要；应牢记于心。他们给出了对于量热完全气体的任意流场，由某一给定点实际的M ,T ,p 和 的值来计算定义的量 和 的公式。正因为其重要性，附录A列表给出了 随马赫数变化的函数关系。（对应 的标准大气条件）;? 临界参数的定义与计算公式 临界参数的定义： Consider a point in a general flow where the velocity is exactly sonic, i.e. where M=1. Denote the static temperature ,pressure, an density at this sonic condition as T*,p*, and ρ*,respectively. 考虑流场中速度为准确的音速这一点，即M=1 的点。我们定义这一点（音速条件）的静温、静压、静密度定义为临界参数，用T*、p*和ρ*表示。;? 特征马赫数（速度系数）M*的定义及计算公式;下面利用能量方程(8.35)得到M与M*的关系：;There, M* acts qualitatively in the same fashion as M except M* approaches a finite value when the actual Mach number approaches infinity.;小结： In summary, a number of equations have been derived in this section, all of which stem in one fashion or another from the basic energy equation for steady, inviscid, adiabatic flow. 8.5 WHEN IS A FLOW COMPRESSIBLE? 什么条件下流动是可压缩的？ We have stated several times in the preceding chapters the rule of thumb that a flow can be reasonably assumed to be incom