《工程流体力学》01 第一章.ppt

School of Jet Propulsion Beihang University. Chapter 1 Introduction 1.1 Preliminary Remarks When you think about it, almost everything on this planet either is a fluid or moves within or near a fluid. -Frank M. White The concept of a fluid A solid can resist a shear stress(剪切应力) by a static deformation, a fluid can not. Any shear stress applied to a fluid, no matter how small, will result in motion of that fluid. The fluid moves and deforms continuously as long as the shear is applied. What is Fluid Mechanics Fluid Mechanics is the study of fluid either in motion (Fluid Dynamics 流体动力学) or at rest(Fluid Statics 流体静力学) and subsequent effects of the fluid upon the boundaries, which may be either solid surfaces or interfaces with other fluids. History and Scope of Fluid Mechanics Pre-history: Sailing ships with oars(橹桨) and irrigation system were both known in prehistory Archimedes(285-212 BC) Parallelogram law for addition of vectors Leonardo da Vinci(1452-1519) * Equation of conservation of mass in one-dimensional steady flow Isaac Newton(1642-1727)  19th century Navier (1785-1836) Stokes (1819-1905) N-S equation viscous flow solution 1.2 The Fluid as a Continuum (连续介质） 1.3 Some Properties of fluids 1.viscosity(粘性) * Definition： When a fluid is sheared（剪切）, it begins to move. Subsequently, a pair of forces appear on the shear surface, which resists the shear motion of the fluid. This is called viscosity m : Coefficient of viscosity (粘性系数)[FT/L2] n = m / r: Kinematic viscosity (运动学粘性系数)[L2/T] 2. Compressibility(压缩性) Incompressible(不可压): r = const Most liquid flows are treated as incompressible. Only 1 percent increase if pressure increase by 220 4.Thermal Conductivity(热传导) 1.4 Two different points of view in analyzing problems in mechanics * The Eulerian view (欧拉观点)and the Lagrangian view （拉格朗日观点） The Eulerian view is concerned with the field of flow, appropriate to fluid mechanics.