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Solution diverge with small element size.

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Old   October 22, 2013, 15:36
Default Solution diverge with small element size.
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salvatore
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Hi All

I am using FLUENT to study the flow in an aorta. Specifically, I am performing a mesh quality analysis to assess the best element size and the optimal value of wall shear stress.

The problem is that the solution diverge with small element size. Specifically, a mesh with 700000 element (skewness is about 0.75) shows convergence while meshes with 1400000 (skewness is about 0.84) elements or 2100000 elements (skewness is about 0.86) show divergence.

Meshes with high number of elements diverge using either Simple or Piso algorithm at 3e-4 of residuals. The model has an inlet (velocity inlet) and four outlet with flow split boundary conditions (outflow), and the flow is assumed laminar.

Does anyone has suggestions on my problem?

Many thanks
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Old   October 23, 2013, 07:19
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Vignesh KPV
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Try adjusting your relaxation factors
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Old   October 23, 2013, 16:13
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Thank you very much for your suggestion!. I have decreased the under relaxation factor for moment to 0.1... should I decrease more?.... by the way, I will work on it and let you now... thanks
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Old   October 25, 2013, 12:09
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Maybe the assumption of laminar flow does not hold.
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Old   October 26, 2013, 05:48
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I fixed it!!... apparently the problem was that I have split the mesh in several zones.... Once I have merged all fluids in the analysis, the solution converged rapidaly
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