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Unformatted text preview: 1 External Flow Fluid Dynamics Application III External Flow Chapter 11 Drag & Lift Definition of Drag & Lift Concept of Separation & Wake 1 Drag coefficient & Influence Factors Depends on boundary factor, classified as Internal flow: fluid is entirely bounded External flow: flow is unconstrained spatially on Classification of Fluid Motions length scale relevant to body Openchannel: top surface of the fluid flow is exposed to atmosphere 2 2 Definition of Drag & Lift  I Incoming flow FREE STREAM , with uniform flow velocity U uniform flow velocity U passes over a 2D object Forces from surrounding fluid on this 2D object are: ( a ) pressure force, F dA p ) ( r 3 ( b ) viscous force, (Pressure is gage pressure) ( ) dA w r Definition of Drag & Lift  II Resultant force on body Force F decomposed into Horizontal component ( ) dA dA p F w + = r r r ) ( L D F F F L D r r r r r + = + = Horizontal component  drag Vertical component Lift Drag = pressure drag + viscous drag 4 ( ) dA p D w + = sin cos Drag is a resistance force, opposite to flow direction 3 Shear force on object surface Is caused by shear between fluid & solid surface (due to & velocity gradient Shear Force & Viscous Drag (due to & velocity gradient ) Is a function of ___________and ______of the object Also known for viscous drag , friction drag surface area length = du/dy 5 w = .(du/dy) Drag = pressure drag + viscous drag ( ) dA p D w + = sin cos Separation often occurs at sharp corners...
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This note was uploaded on 05/22/2011 for the course ME 132 taught by Professor Dongmeizhou during the Spring '11 term at CSU Sacramento.
 Spring '11
 DongmeiZhou
 Fluid Dynamics

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