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 3xm=. (c) What is the average gradient, in Pa/m, in this section? Solution: For air at 20°C, take 31.2kg mρ=and 51.8 10kg m sμ−=×⋅. Using laminar boundary layer theory, compute the displacement thickness at 3xm=: ()551.2 2 3Re4 101.8 10xUx−===××(laminar) *1251.721 31.7210.0082Re410xxmδ≈×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.