polymer - "drag" reduction in pipe flow For a...

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For a given Re, is there anyway to have a friction factor less than that for a smooth pipe? “drag” reduction in pipe flow
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• Pierre Du Buat (1734 – 1809) believed that fluid in contact with surface invariably formed a stagnant layer over which the rest glided Regardless of the surface roughness • Henry Darcy (1857) demonstrated the importance of roughness in determining pipe flow resistance.
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smooth pipe K s /D = ε /D = 0.0726/12.7 = 0.006; Rohr K s /D = ε /D = 0.1143/50.8 = 0.002: Liu riblets riblets Skin Friction Drag Reduction via riblets
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Silky shark Caroharhinus falciformis 3M-riblets Shark scales are 0.2 – 0.5 mm in height and are aligned in flow direction ridge spacing may be from 35 – 105 μ m
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Johnson (1970): Large drag measured - probably due largely to the rough, sandpaper-like skin of the shark Bechert (1985) It appears that the fins might have produced enormous parasitic drag and/or the dead sharks may not have been towed at zero angle of attack.”
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s + = su*/ ν
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h + = hu * / ν s + = su * / ν h = s
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1% -2% reduction in fuel if 70% of airplane covered - French Airbus -
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polymer - "drag" reduction in pipe flow For a...

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