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Depth for 2D problems

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Old   February 4, 2004, 05:01
Default Depth for 2D problems
  #1
Jamcam
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Hi all,

In the 'Reference Values' panel, you can set a 'depth' variable which is applicable to 2D problems only. I would assume this is a kind of Z coordinate value?

Does anyone know how to correctly determine the value for depth? My 2D grid for flow past a cylinder has a height of 3 and a length of 6, so what is the correct value for depth in this case?

I've thoroughly searched the Fluent online help, but there is very little on this.

Thanks in advance

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Old   February 4, 2004, 08:44
Default Re: Depth for 2D problems
  #2
ap
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FLUENT assumes a "depth" for 2D simulations which is the unit of lenght you're using. If you use meters, depth is 1 meter.

Hi

ap
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Old   February 4, 2004, 10:49
Default Re: Depth for 2D problems
  #3
Jamcam
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Thanks for responding, ap.

How do I define the correct depth for a domain 3m in the Y direction and 6m in the x direction?

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Old   February 4, 2004, 15:34
Default Re: Depth for 2D problems
  #4
ap
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I don't know if it's possible to change the depth in a 2d case. If do a 2D simulation, you decide not to consider it.

Hi

ap
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Old   February 5, 2004, 03:59
Default Re: Depth for 2D problems
  #5
Vladimir Krejci
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Hi go for menu Report > Reference Values you can set something like that you want there but I would read the manual
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Old   February 5, 2004, 04:39
Default Re: Depth for 2D problems
  #6
Jamcam
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The problem is that the manual does not give any indication of how to calculate the depth in the reference values panel.

I've been varying the value for my flow past a cylinder simulation and it directly effects the drag coefficient on the cylinder. In other words, I can get any drag coefficient value I like by varying this parameter!
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Old   February 5, 2004, 05:19
Default Re: Depth for 2D problems
  #7
Rob Hart
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As far as I can tell, fluent just multiplies things appropriately by the depth.

So if I ask for the total force on a boundary, it is multiplied by the "depth" (i.e. if I double the depth, the force is double), but if I ask for average pressure, it is unaffected.

Where exactly do you get your drag coefficient from? I would have thought depth should cancel out and it would remain constant.

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Old   February 5, 2004, 05:26
Default Re: Depth for 2D problems
  #8
Rob Hart
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Look at: "26.3.1 Computing Forces and Moments." in the user guide.

"The force coefficient is defined as force divided by [(1/2)rhoV^2A] , where rho, v, and A are the density, velocity, and area explicitly specified in the Reference Values panel."

In other words if you mess around with the "depth" value, (which will increase your force) then you should also mess with the "area" value.

I think this means you will only get the correct coefficient if you explicitly set the reference values to fit your case.

Rob
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Old   February 5, 2004, 05:51
Default Re: Depth for 2D problems
  #9
Jamcam
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Cheers Rob,

I'll look into that!
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