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Convergence issue in CHT simulation

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Old   May 8, 2015, 14:33
Lightbulb Convergence issue in CHT simulation
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Deepak
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Hi All,

For my first CFD simulation, I was required a simulate a CHT system for NATURAL CONVECTION. The system has 2 components - plastic tube (almost U-shaped)and a heat sink. The heat sink snugly fits into the open face (along the length), such that the both together form a hollow tube with fins of the heat-sink in the air passage. The was to study the temperature distribution over the system at steady-stage.

When I start the simulation, for some reason all the residuals don't seem to decrease (see attachment). I have attached the images of geometry, mesh, and the residuals plot. I am not sure where I am going wrong. I need help!

mesh.jpg

residuals.PNG

setup.jpg

geometry.jpg

Deepak
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Old   May 8, 2015, 21:56
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I might not be the best person to give advice on how to converge a CHT problem (see my other post), but you could try refining your mesh in the fluid domain (and adding more inflation layers). I'm assuming that your opening boundary conditions are asserting a pressure drop along the channel (and hence a flow)?
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Old   May 8, 2015, 22:47
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Alg,

Its a natural convection problem. The ends of the tube are open to atmospheric pressure.

Like you suggested, I increased the number of inflation layers (to 5), and it did not help. Thanks for the inputs.
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Old   May 8, 2015, 23:11
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Ok, no worries.

How are your opening boundary conditions set then? and which way does your gravity vector point? I've run a similar simulation recently but modelled a fuild domain 'around' the channel, linking the inlet and outlet, with openings on the outer surfaces of this larger domain. This avoided the situation where you have a pressure set at each end of the channel, which will dictate the mean flow. There may be an easier way to do this though...
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Old   May 9, 2015, 07:48
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Before we dive into details on this simulation - have you read the FAQ on this issue? http://www.cfd-online.com/Wiki/Ansys...gence_criteria
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cfx, conjugate heat transfer, fins, heatsink, natural convection

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