External Incompressible Viscous Flow
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Transcript of External Incompressible Viscous Flow
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EXTERNAL INCOMPRESSIBLE VISCOUS FLOW
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Details of viscous flow around an airfoilBoundary Layer Concept
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Boundary layer thickness definitionsBoundary layer on a flat plateDisplacement ThicknessMomentum Thickness
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Boundary layer thickness definitions
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Displacement Thickness (d *)Displacement Thickness and Momentum Thickness
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Method of AnalysisExact solution - Only for laminar BL- Using Blasius (1908) solution
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General Form of Momentum Integral Equation
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Alternative Form of Momentum Integral EquationThis equation is valid for: Steady flow Incompressible flow 2-D flow No body force
Can be applied for LAMINAR and TURBULENT boundary layers.
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where H = d*/q Velocity-profile "shape factor". Alternative Form of Momentum Integral Equation
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Zero Pressure Gradient BLwhere u/U = velocity distribution and usually is expressed as u/U = f (y/d), also d = d (x).
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AssumptionsDimensional AnalysisDarcy-Weisbach equation The above equation is valid for laminar and turbulent BL, with assumptions: 1. Steady flow 2. Incompressible flow 3. 2-D flow 4. No body forces 5. dp/dx = 0.
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How to solve the BL equation? Assume a velocity profile: u/U = f (y/d), with B.Cs:at y = 0, u = 0, at y = d, u = U, at y = d, u/y = 0.
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How to solve the BL equation?
The MIE becomes:
Finally:tw = f(d), and d = d (x).
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The rate of growth of the BL For laminar BL flow:For turbulent BL flow:The turbulent BL develops more rapidly than the laminar BL.
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Skin Friction Coefficient (Cf)Cf is defined as:
For laminar BL flow:For turbulent BL flow:tw in the turbulent BL is much higher than in the laminar BL
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Velocity Profiles
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Fluid Flow about Immersed Bodies Total force:
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Drag ForceDrag (CD) coefficient is defined as:
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Lift Force