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convergence problem of chtMultiRegionFoam in simulation of free convection

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Old   May 1, 2017, 12:50
Default convergence problem of chtMultiRegionFoam in simulation of free convection
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Dear Foamers,

I simulated free convection of air in a vertical channel. You can find simulation results of the thermal and viscous boundary layers in the attached pictures.

The simulated domain is a 125mm x 40 mm 2D rectangle with:
The front and back boundary as "empty",
The left and right boundary are "symmetryPlane"
The upper boundary is "pressureInletOutletVelocity" for velocity, "zeroGradient" for p_rgh and temperature,
The lower boundary has "inletOutlet" for velocity and temperature, and "totalPressure" for pressure.

A heater of 85mm tall in the vertical direction and 0.25mm thick in the horizontal direction is attached to the left boundary. fvOption was applied to add a heat source to the heater.

The simulation ran well before the maximum temperature was achieved, as shown in the pictures. I would expect the temperature to reach a steady state, but the temperature began to decrease, while the Courant number continued to increase to far above 1. As you can see in the attached animation, the thickness of the boundary layer shrank rapidly to almost zero.

The original mesh was 0.25 to 1.6mm/cell the horizontal direction, and 1.25mm/cell in the vertical direction. I double the mesh density, and the maximum temperature was achieved at the same runTime and had the same value. Afterwards the temperature decreased, and the boundary layer shrank in a similar manner although with a much slower rate.

I am not sure whether this computation deliver the correct results. Does anyone know why the temperature reduces after the maximal was achieved? I would appreciate for any comments and suggestions!

Thank you very much in advance!

Best regards,
sitajeje
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File Type: jpg BLU.jpg (31.5 KB, 9 views)
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File Type: zip BLwrongT.zip (134.2 KB, 2 views)

Last edited by sitajeje; May 1, 2017 at 16:39.
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Old   May 1, 2017, 13:29
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Arvind Jay
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Is part of the left boundary wall? If so, the contours look correct.
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