PTT 204/3 APPLIED FLUID MECHANICS SEM 2 (2012/2013)

1. PTT 204/3APPLIED FLUID MECHANICSSEM 2 (2012/2013) Chapter 1: Introduction and Basic Concepts

2. OBJECTIVES • At the end of this chapter, you should be able to: • Understand the basic concepts of fluid mechanics and recognize the various type of fluid flow problems encountered in practice.

3. 1-1 What is fluid mechanics? • The science that deals with the behavior of fluids at rest (fluid statics) or in motion (fluid dynamics), and the interaction of fluids with solids or other fluids at the boundaries. • It is divided into several categories: Examples: hydrodynamics, hydraulics, Gas dynamics, aerodynamics etc.

4. Hydrodynamics: The study of the motion of fluids that can be approximated as incompressible (such as liquids, especially water, and gases at low speeds). • Hydraulics: A subcategory of hydrodynamics, which deals with liquid flows in pipes and open channels. • Gas dynamics: Deals with the flow of fluids that undergo significant density changes, such as the flow of gases through nozzles at high speeds. • Aerodynamics: Deals with the flow of gases (especially air) over bodies such as aircraft, rockets, and automobiles at high or low speeds. • Meteorology, oceanography, and hydrology: Deal with naturally occurring flows.

5. What is FLUID? • A substance in the liquid or gas phase is referred as FLUID • The following general descriptions of liquids and gases: • Gases are readily compressible. • Liquids are only slightly compressible (incompressible).

6. Fluid Properties • Common properties: pressure, temperature, mass, volume, density. • Other fluid properties: specific weight, density, specific gravity, surface tension and viscosity. • It is also important in determining the character of the flow of fluids and the amount of energy that is lost from a fluid flowing in a system.

7. Stress on fluid • Stress=force per unit area. Normal stress, σ = Fn/dA (in fluid at rest, it is called pressure) Shear stress, τ = Ft/dA (for fluid at rest=0)

8. 1-2 Application areas of Fluid mechanics Examples: • Natural flows & weather • Aircraft & spacecraft • Boats • Human body • Piping & plumbing systems • Wind turbines • and many more…..

9. Weather & Climate Tornadoes Thunderstorm Global Climate Hurricanes

10. Vehicles Surface ships Aircraft Submarines High-speed rail

11. Environment River hydraulics Air pollution

12. Physiology and Medicine Blood pump Ventricular assist device

13. Sports & Recreation Water sports Cycling Offshore racing Auto racing Surfing

14. 1-3 No-Slip Condition • A fluid in motion comes to a complete stop at the surface and assumes a zero velocity relatives to the surface. • Fluid in direct contact with solid “sticks” to the surface due to viscous effect, and there is no slip.

15. THE NO-SLIP CONDITION A fluid flowing over a stationary surface comes to a complete stop at the surface because of the no-slip condition. The development of a velocity profile due to the no-slip condition as a fluid flows over a blunt nose. Flow separation during flow over a curved surface.

16. 1-4 Classification Of Fluid Flows A. Viscous vsinviscid regions of flow • Viscosity -a measure of internal stickiness of fluid • Viscous flow region–significant frictional effect • Inviscid flow region – negligible viscous forces The flow of an originally uniform fluid stream over a flat plate, and the regions of viscous flow (next to the plate on both sides) and inviscid flow (away from the plate).

17. Classification Of Fluid Flows B. Internal vs external flow • Internal flow – the flow in a pipe or duct where fluid is completely bounded by solid surfaces. • External flow - the flow of unbounded fluid over a surface such as a plate, a wire or a pipe. C. Compressible vs incompressible • Incompressible flow – almost constant density throughout - liquids • Compressible flow - gases D. Laminar vs turbulent flow • Determined by Reynolds number, Re • Re < 2000 (laminar); Re > 6000 (turbulent); between laminar and turbulent is transitional

18. Classification Of Fluid Flows • Natural (or unforced) vs forced flow • Natural flow – the fluid motion due to natural means such as the buoyancy effect • Forced flow – the fluid is forced to flow over a surface or in a pipe by external means such as pump or fan F. Steady vs unsteady flow • Steady = no change of properties (velocity, temperature, etc) at a point of time • Unsteady = opposite of steady • Transient = typically used for developing flows, ( e.g. pressure build up inside rocket engine, until it operates steadily)

19. SYSTEM AND CONTROL VOLUME • System: A quantity of matter or a region in space chosen for study. • Surroundings: The mass or region outside the system • Boundary: The real or imaginary surface that separates the system from its surroundings. • The boundary of a system can be fixed or movable. • Systems may be considered to be closedor open. • Closed system (Control mass): A fixed amount of mass, and no mass can cross its boundary.

20. Open system (control volume): A properly selected region in space. • It usually encloses a device that involves mass flow such as a compressor, turbine, or nozzle. • Both mass and energy can cross the boundary of a control volume. • Control surface: The boundaries of a control volume. It can be real or imaginary. An open system (a control volume) with one inlet and one exit.

21. Quiz time Good luck!

22. Please answer the following questions…. • What is fluid? • Stress is force per unit area. Name 2 types of stress in fluid and their equations. • Give 3 examples of application areas of fluid mechanics. • Please explain about the “no-slip condition”. You have 15 minutes. TQ!