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Where / how are cell variables evaluated?

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Old   February 5, 2018, 12:55
Default Where / how are cell variables evaluated?
Tyler Richardson
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Question is straight forward but here is some background:

I am evaluating an existing UDF (DEFINE_HEAT_FLUX) to calculate the wall HTC. I do not particularly like the results, so I wanted to go and look on a simple pipe problem how the HTC is evaluated.

I can tell that the UDF is using C_U(c0,t0), C_V(c0,t0), and C_W (c0,t0) to calculate the bulk fluid velocity.

As far as I can tell, this is taking the velocity in the cell adjacent to the wall, which very well may be in the boundary layer, and velocity may not represent the bulk fluid velocity.

In order to prove this, I went to look at the velocity distribution through the first element on the wall, and grabbed the velocity at the center of this first element to try and re-do the calculation. I don't really get the right result.

So I am wondering how / where the C_U, C_V, C_W are evaluated such that I can probe them on my X-Y plot to re-calculate the HTC (by hand) and compare to what fluent calculated with the UDF.

Any help would be greatly appreciated
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cell variables, heat transfer, heat transfer coefficient, htc, udf

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