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Mesh influence in convergence

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Old   September 29, 2017, 10:44
Default Mesh influence in convergence
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oswaldo borjas
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Hi there,

Im a beginner in CFD simulations. For a final project, i am modeling a turbulent flow across a pipe (CS). In the middle of pipe, exist a heat flux
I need to find the output values of temperature across the pipe.

In the beginning, i started with a 3D model. Then in order to make simple the model, i change the 3D model to 2D model.

The problem is when i apply a fine mesh (refining the most important study areas) the solution never converge, eventhough if i set to 10000 the iteration number).

In the other hand, if i set a coarse mesh the solution converge (around 500 iterations)

I dont know if the problems is because of Boundary conditions or the course of mesh

BC
The inner diameter of pipe is 58.8 mm
Velocity inlet : 25.78 m/s
Pressure outlet: 1 bar
Heat Flux:4200 W/m2

I am using a K-Epsilon standard model and the fluid is AIR (ambient conditions). I reviewed all the input parameters to be sure if i am making a mistake but it seems everything Ok.

The main questions is:
Is the refine of mesh an important value for the model convergence?

I think the most important values are the BC parameters

Thanks in advance!

Coarse mesh
https://www.dropbox.com/s/oiwepa06z3...0mesh.jpg?dl=0

Fine mesh
https://www.dropbox.com/s/i4ixtw6kny...203mm.jpg?dl=0

No convergence
https://www.dropbox.com/s/agm9jxz0q5...encia.jpg?dl=0
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Old   October 3, 2017, 09:13
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power
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Did you check quality parameters of mesh?
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Old   October 3, 2017, 09:26
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Filippo Maria Denaro
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That could also depend on the type of RANS model you are using
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boundary conditions, convergence, mesh, pipe, refine

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