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Old   March 10, 2015, 22:49
Default Discontinuity across interfaces
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I need your help, experts.

I am using several domains connected by domain interfaces in my simulation, heat diffusion with an internal electrical source (see attached file 'Mesh and Geometry).

All external sides of the assembly insulated, except one on the right hand side. Therefore, during t > 0 s, there is a temperature gradient in the -Z direction. Heat is generated by applying electrical potential across the assembly in Z direction. For a simplicity reason, I set same properties and initial conditions at each domain. Mesh connection type at the interfaces is GGI. The interface model is General Connection, with thermal resistance and electrical resistance set to zero, as I assume that all domains are part of one assembly. During calculation, I checked the convergence of my solution at each time step. The convergence criteria (10^-6) was met using the double precision.

Finally, I compared the temperature in the Z direction calculated by CFX with a 1D analytical solution, given in by Carslaw and Jaeger, and found very good agreement, no discontinuities of temperature across the interfaces in the Z direction.

However, I found that there is a minor discontinuity across the interfaces in the Y direction.

In addition, there is unrealistic power accumulation on the left hand side of my geometry. I reckon the discontinuity across the interfaces in the Y direction and power skewness are interrelated. What can be the reasons of this problems? Is the problem in mesh? What would be the best way to mesh such an assembly? Any other possible pitfalls?

Looking forward for your replies.


Last edited by Nurzhan; March 11, 2015 at 01:58.
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Old   March 10, 2015, 23:42
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Glenn Horrocks
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Your image was not posted so I cannot see what you are modelling. So I cannot say anything about the Y discontinuity.

But let me guess about the power accumulation - simulations like this often need convergence on residuals AND imbalances. Are your imbalances small? You might just need to converge more until the imbalances are OK. Most people are happy with 1% imbalance but your requirements may be tighter or looser.
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Old   March 11, 2015, 01:59
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Hi Glenn,

thanks for your prompt reply.

My conservation target is 1%, I will try to make smaller first then.

In addition, you can still open the above pictures if make a write click and select open image. Anyway, I tried to reload the pictures but it failed again.

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