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Dre August 1, 2008 11:06

2D Drag Coefficient
 
So I'm having problem trying to figure out what to do with the area term in the drag coefficient formula.

Since it's in 2D, you usually replace the area term with just the diameter (in this case for a cylinder).

But now with CFX, since you can't really do a 2D simulation, do you just take the diameter, or do you need to take into consideration the thickness of that one element?

Glenn Horrocks August 3, 2008 18:39

Re: 2D Drag Coefficient
 
Hi,

2d drag coefficient of what?

These relations need a representative length. For a sphere or cylinder the diameter is th obvious length, for a square the length of the side. How you model it is totally separate.

Glenn Horrocks

Dre August 4, 2008 16:11

Re: 2D Drag Coefficient
 
I am modelling a cross section of a cylinder.

My problem is do I take the frontal area, or do I take the diameter.

Since it's 2D, I should take the diameter, but since it's in CFX, do I take the diameter multiplied by the thickness of the element?

Glenn Horrocks August 4, 2008 21:55

Re: 2D Drag Coefficient
 
Hi,

I think you will find the diameter equals the frontal area. It did last time I looked at a cylinder anyway.

Most of these coefficients use unit length, in SI units that is 1 metre. If your element thickness is different to a metre then you need to scale the forces to account for that.

Glenn Horrocks


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