Lecture_1_Introduction and Basic Concepts

Lecture_1_Introduction and Basic Concepts - EGN 3353C Fluid...

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Unformatted text preview: EGN 3353C Fluid Mechanics Chapter 1: Introduction and Basic Concepts Lecture 1 (Read Chapter 1 of C&C) ! What is fluid mechanics? o Study of fluids at rest " statics o Study of fluids in motion " dynamics ! What is a fluid? o A liquid or a gas o Distinction between a solid and a fluid A fluid continuously deforms under the application of the shear stress " a fluid cannot sustain a shear stress and remain at rest. No slip BC " fluid in contact with a solid boundary has Solid resists an applied shear stress by deforming same velocity as boundary. This means that the fluid on the top surface moves with same velocity as surface, while fluid on lower stationary surface has zero velocity. Lou Cattafesta MAE Dept. University of Florida EGN 3353C Fluid Mechanics You can buy this CD-ROM at http://www.cambridge.org/uk/catalogue/catalogue.asp?isbn=0521604761 ! What is the difference between a liquid and a gas? Liquid " molecules are free to move about the container but retains the shape of the container (and forms a free surface between the liquid and gas boundary) due to strong cohesive forces (e.g., water, oil, glycerin, mercury) Gas " molecules are not restricted to container due to weak cohesive forces (air, helium, nitrogen, hydrogen) Lou Cattafesta MAE Dept. University of Florida EGN 3353C Fluid Mechanics (a) Solid very strong intermolecular forces (b) Liquid moderate intermolecular forces (c) Gas very weak intermolecular forces ! Classification of Fluid Flows Lou Cattafesta MAE Dept. University of Florida EGN 3353C Fluid Mechanics o Viscous versus by inviscid flow" of characterized importance viscosity or fluids internal stickiness (i.e., its resistance to motion) in certain regions of a flow o Internal vs. external flows vs. o Compressible vs. incompressible # Characterization of flow density changes in a flow due to pressure o A flow (not a fluid substance) is incompressible or compressible vs. Lou Cattafesta MAE Dept. University of Florida EGN 3353C Fluid Mechanics o Examples of compressibility effects " high Mach number Ma = V c flow and sound & o Laminar vs. turbulent flow Lou Cattafesta MAE Dept. University of Florida EGN 3353C Fluid Mechanics o Natural (convection) vs. force convection flow vs. Lou Cattafesta MAE Dept. University of Florida EGN 3353C Fluid Mechanics o Steady (no time variation in the flow pattern) vs. unsteady (time variation) flow ! Above a flow Reynolds number Re = Vd / of about 40, the flow behind unsteady. a cylinder becomes Below that, the flow pattern doesn't change with time. Lou Cattafesta MAE Dept. University of Florida EGN 3353C Fluid Mechanics ! Mathematical Modeling of Fluid Mechanics Problems o We solve fluid mechanics problems using conservation laws 1. conservation of mass 2. conservation of momentum (linear and angular) 3. conservation of energy (1st Law of Thermodynamics) 4. supplemental information (2nd Law of Thermodynamics, equation of state (e.g., ideal gas law)) ! You are responsible to review the rest of Chapter 1 that discusses a closed system vs. an open control volume (as in Thermodynamics) and units and dimensions and significant digits (see notes on web site). Lou Cattafesta MAE Dept. University of Florida ...
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