How do i find the drag coefficient of a cube?

Discussion in 'Physics & Math' started by MatthewLiem, Jan 14, 2007.

  1. MatthewLiem Registered Member

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    3
    The length of one side of the cube is 20cm. I need the drag coefficient to find out to determine my drag force of this object.
    Thanks!

    -matt
     
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  3. James R Just this guy, you know? Staff Member

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    There's no easy way that I know of. It will depend on what the cube is made of, what fluid it is moving in, etc.

    Most likely, it will be something between 0.5 and 1, though.
     
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  5. Absane Rocket Surgeon Valued Senior Member

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    I have no idea how to calculate it, but I am sure it depends on how the cube is moving through the cube. It could move like an arrow or one could push it through like like how a brick falls.. flat end perpendicular to the air flow.
     
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  7. Pete It's not rocket surgery Registered Senior Member

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    Why? I thought the shape, size, and orientation would be enough?
     
  8. CANGAS Registered Senior Member

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    Drag coefficients have traditionally been derived empirically in wind tunnels.

    Because aerodynamics is exact mathematical science.

    Partly. And the second part is black magic voodoo.

    The drag coefficient will depend crucially upon what the orientation of the cube to the wind direction is, assuming that the cube is maintained in a stable orientation. Every different angle to the wind direction will give a different coefficient. And if the cube is free of rigid support and is allowed to tumble freely, you have a very complicated problem. A freely tumbling cube would be virtually impossible to model theoretically and would have to be solved empirically by a statistically significant number of free-fall experiments. Of course, if you can hack into one of A51's Crays then you might be able to solve it theoretically.

    And, yes Virginia, the composition of the cube really will have a probably small effect on the drag coefficient because the surface texture may make a measureable difference in how easily air flows past it. But no guessing here; sometimes a smooth texture has less drag and sometimes a rough texture has less drag.
     
  9. Pete It's not rocket surgery Registered Senior Member

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    Ah yes. I didn't consider surface texture. Although I'd put that in its own explicit category rather than with composition.
     
  10. CANGAS Registered Senior Member

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    It was a close call for me, practically the flip of a coin; different compositions with identical textures should yield identical coefficients.
     
    Last edited: Jan 14, 2007

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