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Drag Force at very very high Renolds Number ?

  1. Jul 25, 2011 #1
    What is the expression for Drag Force at very very High Renolds Number flow (>10^6)
    as we know the expression
    for drag force between Re1 and Re10^5 = 0.5kpAv^2
    but this isnt valid aft 10^5 ..
    so .....
     
  2. jcsd
  3. Jul 25, 2011 #2

    boneh3ad

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    There isn't any general equation for drag at any value of Reynolds number to be honest. Even the equation you quoted depends on a a coefficient that varies wildly for different environments and geometries.

    Let me instead pose this question: what exactly is the situation that you are in? What are the details of the system? How high do you consider "very very high," because 10^6 is actually pretty low for quite a few situations.
     
  4. Jul 25, 2011 #3
    as in lets take an example for a sphere of radius 0.1 m moking with the speed of 100 m/sec
    Renolds = pv/viscosity which gives 10^7

    so what wud be the drag force calculating expression for this situation
     
  5. Jul 25, 2011 #4

    boneh3ad

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    It depends on how accurate you want to be. You could use the old formula for a ballpark estimate, or you could go through the long, complicated process of finding pressure drag including the separated regions and viscous drag. It all depends on what you want.
     
  6. Jul 25, 2011 #5
    Since when is this not valid for Re > 10^5?

    As long as you know your drag coefficient this equation is completely valid.
     
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