18932444-Fluid-Mechanics-Lecture-Notes-I - 1 Department of...

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Unformatted text preview: 1 Department of Mechanical Engineering The University of Hong Kong Foundations of Engineering Mechanics ENGG1010 (2008 2009) "Mechanics of Fluids" Lecturer: Dr. C.O. Ng (office: HW7-1; phone: 28592622; email: cong@hku.hk) Required Text : Fundamentals of Fluid Mechanics 5 th Ed., B.R. Munson, D.F. Young & T.H. Okiishi, Wiley Asia Student Edition. References : 1) Fluid Mechanics: Fundamentals and Applications , Y.A. Cengel & J.M. Cimbala, McGraw-Hill. Highly recommended. 2) Fluid Mechanics 6 th Ed., F.M.White, McGraw-Hill. Assessment : In-course continuous assessment 10% - mid-term quiz (details to be announced in due course) Examination 90% Topics Covered : 1. Properties of fluids Definition of a fluid Density Viscosity Surface tension Compressibility 2. Hydrostatics Hydrostatic pressure distribution Pressure measuring devices (manometers) Hydrostatic force acting on submerged plane and curved surfaces Equilibrium of a hydraulic structure under hydrostatic and applied forces 3. Fluid in Motion Continuity equation (conservation of mass) Bernoullis equation (conservation of mechanical energy) Momentum equation (force and rate of change of momentum) Applications o Velocity measurement with a Pitot tube o Jet issuing from an orifice o Flow-rate measurement with a Venturi-meter o Impact force by a jet on a flat plate o Impact force on a pipe bend (I) INTRODUCTION What is Fluid Mechanics? First, what is a fluid ? Three common states of matter are solid, liquid, and gas. A fluid is either a liquid or a gas . If surface effects are not present, flow behaves similarly in all common fluids, whether gases or liquids. Formal definition of a fluid - A fluid is a substance which deforms continuously under the application of a shear stress . o Definition of stress- A stress is defined as a force per unit area, acting on an infinitesimal surface element. o Stresses have both magnitude (force per unit area) and direction , and the direction is relative to the surface on which the stress acts. o There are normal stresses and tangential stresses. normal stress shear stress n t F dA F dA = = o Pressure is an example of a normal stress, and acts inward, toward the surface, and perpendicular to the surface. o A shear stress is an example of a tangential stress, i.e. it acts along the surface, parallel to the surface. Friction due to fluid viscosity is the primary source of shear stresses in a fluid. o One can construct a free body diagram of a little fluid particle to visualize both the normal and shear stresses acting on the body: Free body diagram for a fluid particle at rest. Consider a tiny fluid element (a very small chunk of the fluid) in a case where the fluid is at rest (or moving at constant speed in a straight line). A fluid at rest can have only normal stresses, since a fluid at rest cannot resist a shear stress. In this case, the sum of all the forces must balance the weight of the fluid element. This condition is balance the weight of the fluid element....
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This note was uploaded on 02/02/2010 for the course ME 3600 taught by Professor Kamman during the Fall '09 term at Western Michigan.

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18932444-Fluid-Mechanics-Lecture-Notes-I - 1 Department of...

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