有机无机化学化工热力学教学课件流体流动现象.pptxVIP

1 CHAPTER 3Fluid Flow Phenomena 流体流动现象 2 Content 3.1 INTRODUCTION 3.2 LAMINAR FLOW层流, SHEAR RATE剪切速度, AND SHEAR STRESS剪应力 3.3 RHEOLOGICAL PROPERTIES OF FLUIDS 流体的流变性 3.4 VISCOSITY 黏度 3.5 TURBULENCE湍流 3.6 BOUNDARY LAYERS边界层 3 3.1 INTRODUCTION 1. Ideal fluid and actual fluid(viscous fluid ) 2. Potential flow 势流 3. Viscous flow 粘性流 4. Velocity field 速度场 4 1. Ideal fluid and actual fluid(viscous fluid ) An ideal fluid is one that is incompressible and has no viscosity. Ideal fluids do not actually exist, but sometimes it is useful to consider what would happen to an ideal fluid in a particular fluid flow problem in order to simplify the problem 5 Viscous fluid—All fluids are viscous actually. A fluid for which the molecular viscous effects of diffusion and dissipation can have significant effects on the flow. 6 The behavior of a flowing fluid depends strongly on whether the fluid is under the influence of solid boundaries. Potential flow 势流 Viscous flow 粘性流 7 2. Potential flow(or irrotational flow)势流(或无漩流) (1) Neither circulations nor eddies can form within the stream, so that potential flow is also called irrotational flow; (2) friction cannot develop, so that there is no dissipation of mechanical energy into heat. 理想流体的无漩流动 Potential flow can exist at distances not far from a solid boundary. 8 3. Viscous flow The flow of incompressible fluid under the influence of solid boundaries The effect of the solid boundary on the flow is confined to a layer of the fluid immediately adjacent to the solid wall. This layer is called the boundary layer（边界层）. 9 Potential flow Boundary layer Viscous flow 10 Within the current of an incompressible fluid under the influence of solid boundaries, four important effects appear: (1) the coupling of velocity-gradient and shear-stress fields, (2) the onset of turbulence（湍流）, (3) the formation and growth of boundary layers, (4) the separation of boundary layers from contact with the solid boundary. 11 4. The velocity