08第八章气体的流动精要.ppt

Chapter 8Thermodynamics of High-Speed Gas Flow 第8章 气体和蒸气的流动 8.1 声速与马赫数 Velocity of Sound and Mach Number 8.2 一维定熵稳定流动 One dimensional Isentropic Steady Flow 8.3 喷管出口流速和流量的计算 Outlet Velocity and Flow rate Calculation for Nozzles 8.4具有摩擦的绝热稳定流动 Adiabatic steady flow with friction 8.5 绝热节流 Adiabatic throttling 8.1 声速与马赫数 Velocity of Sound and Mach Number 1. Velocity of Sound or Sonic Velocity 声速 It is the velocity at which infinitesimally small pressure wave travels through a medium. For adiabatic process For Ideal Gas 对于理想气体 2. Mach number 马赫数 定义：流体某一点的运动速度和该点当地声速之比, 以M 表示 Definition: The Mach number, M, is the ratio of the flow speed, c, to the velocity of sound in the same fluid at the same state. It is denoted as M. Varieties of flow 流动的种类 : 　M 1 　 subsonic flow 亚声速流 　M 1　 sonic flow 声速流 transonic flow 临界流 M 1　 supersonic flow 超声速流 M 1 hypersonic 8.2一维定熵稳定流动） One dimensional Isentropic Steady Flow Physical Problem （物理问题） Gas steady flow 气体的稳定流动 2 The flow in short duct with variable cross-sectional area 变截面短管中的流动 3 The process is isentropic, that is, reversible adiabatic process 可逆绝热的流动过程，即定熵流动 2. Mathematical Model 数学模型） For flow in duct with variable cross-sectional area, it is necessary to use differential equations to reveal the relationships between 　 Conservation Equation of Mass 质量守恒方程） Conservation Equation of Energy 能量守恒方程） Equation of State 状态方程 For Ideal Gas 对理想气体） For Real Gas 对实际气体 Process Equation 过程方程） Equation of Entropy 熵方程） For incompressible fluid , 2 . Energy Equation 能量方程 For reversible process 可逆过程 If then ; If then ; 3 Process Equation For ideal gas 对理想气体 For real gas, k is an empirical constant. 对实际气体来说,k是经验常数 1 喷管内参数的变化情况:dc 0, dp 0 To accelerate the flow, a converging nozzle must be used at subsonic velocities; 当来流速度是亚音速时,截面做成渐缩形 the highest velocity can be achieved by converging nozzle is sonic velocity. 渐缩喷管最多可使流速达到音速 a diverging nozzle must be used at supersonic ve