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Temperatures too low near inlets

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Old   February 13, 2007, 14:29
Default Hi, I have two ducts separa
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Helmut Roth
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Hi,

I have two ducts separated by a solid slab. I solve fluid flow in the ducts (on sub meshes) and use the resulting velocities to solve temperature on the whole mesh. The inlets and exterior walls all have fixed value boundary conditions, while the outlets have zero gradient conditions. There is a jump discontinuity where the duct inlets(300K) meet the slab(400K). In the ducts, near the inlets, I get temperatures (291<T<300) below the lowest boundary value. Any ideas?

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Helmut
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Old   February 13, 2007, 14:56
Default Add some non-orthogonal correc
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Hrvoje Jasak
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Add some non-orthogonal correctors - if you remember, I've sent you an E-mail on this a while back.

Regards,

Hrv
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Old   February 13, 2007, 15:16
Default Hello Helmut, Forgot to men
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Hrvoje Jasak
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Hello Helmut,

Forgot to mention: the unboundedness you mention is due to the non-orthogonal correction in the Laplacian. If you feel your mesh should be orthogonal, you can remove the unboundedness by using the following setting for the equation in system/fvSchemes - it specifies that the non-orthogonal correction will not be added:

laplacianSchemes
{
laplacian(gamma,T) Gauss linear uncorrected;
}

(please adjust the name of the laplacian, I cannot guess it).

Also, just using a uniform initial guess for T will help very much - if I remember correctly, you are starting with a step-profile.

Sorry for my forgetfulness,

Hrv
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Old   February 13, 2007, 15:49
Default Hi Hrv, Thanks for the sugg
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Helmut Roth
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Hi Hrv,

Thanks for the suggestions. I'm using a uniform initial temperature, having seen the folly of the step-profile earlier (thanks!). The mesh should be orthogonal (rectangular blocks and simple uniform grading). Anyway, I tried with some nonorthogonal correction, as in your first reply above, and then using Gauss linear uncorrected laplacian schemes, as suggested next. Same results.

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