空气动力学chapter9(1)概念.ppt

* * CHAPTER 9 OBLIQUE SHOCK AND EXPANSION WAVES 斜激波和膨胀波 9.1 引言 第八章我们讨论了正激波, 本章我们讨论斜激波, 及超音速流场中的另一个重要特征—膨胀波。 Wave angle: 激波角, 激波与激波上游来流的夹角。 A normal shock wave is simply a special case of the general family of oblique shocks, namely, the case where the wave angle is 900. β T1 p1 ρ1 M1 1 ② ① Oblique shock a. Concave corner M2 p1 ρ2 ρ1 T2 T1 Expansion fan M2 M1 p2 p1 ρ2 ρ1 T2 1 θ: Deflection angle 偏转角） θ θ Across the oblique shock wave, the Mach number discontinuously decreases, and the pressure, density, and temperature discontinuously increase. 穿过斜激波，马赫数间断地减小，而压强、密度和温度不连续地增加。 Across the expansion wave, the Mach number continuously increases, and the pressure, density, and temperature continuously decrease. 穿过膨胀波，马赫数连续增加，而压强、密度和温度连续减小。 oblique shock wave 斜激波 expansion wave 膨胀波 Hence, an expansion wave is the direct antithesis of a shock wave. 因此，膨胀波是激波的一个正相反的对应物。 Oblique shock and expansion waves are prevalent in two- and three-dimensional supersonic flow. These waves are inherently two-dimensional in nature, in contrast to the one-dimensional normal shock waves discussed in Chap.8. That is, in Fig. 9.1a and b, the flow-field properties are a function x and y. The purpose of the present chapter is to determine and study the properties of these oblique waves. 斜激波和膨胀波在二维、三维超音速流动中是很普遍的。这些波在本质上是二维的，与第八章讨论的一维正激波相反。即，在图9.1a和b中，流场特性是x 、 y的函数。本章的目的就是确定和研究这些斜波（斜激波和膨胀波）的性质。 ? What is the physical mechanism that creates waves in a supersonic flow? 超音速流中产生波的物理机理是什么？ If the upstream flow is subsonic , as shown in Fig.9.2a, the disturbances have no problem working their way upstream, thus giving the incoming flow plenty of time to move out of the way of the body. 如图9.2a所示，如果上游是亚音速的， 扰动可以毫不困难地传播到远前方上游，因此，给了来流足够的时间以绕过物体。 The information is propagated upstream at approximately the local speed of sound. 物体存在的信息以近似等于当地音速的速度传播到上游去。 On the other hand, if the upstream flow is supersonic, as shown in Fig.9.2b, the disturbances cannot work their way upstream; rather, at some fini