Class39_Ex1 - Example Air at 20C and 1atm enters a...

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Example : Air at 20°C and 1atm enters a 40-cm-square duct. Using the “displacement thickness” concept, estimate (a) the core velocity and (b) the mean pressure in the core of the flow at the position 3 x m = . (c) What is the average gradient, in Pa/m, in this section? Solution: For air at 20°C, take 3 1.2 kg m ρ = and 5 1.8 10 kg m s μ . Using laminar boundary layer theory, compute the displacement thickness at 3 x m = : () 5 5 1.2 2 3 Re 4 10 1.8 10 x Ux == = × × (laminar) * 12 5 1.721 3 1.721 0.0082 Re 41 0 x x m δ × Then, by continuity, 2
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This note was uploaded on 12/08/2011 for the course MECHANICS 57:020 taught by Professor Fredrickstern during the Fall '10 term at University of Iowa.

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