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Old   October 12, 2010, 05:14
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Hi all.

I am simulating a free surface flow where the bed is hydraulically rough (several triangles equally spaced). I have already achieved convergence (1o^-5 of residual and 0.01 of imbalance) for a case test where the

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height of the triangles is very small ( I have used the multi grid solver in expert parameter).

Now I am trying to increase the height of the triangles, the height of the water and the height of the domain to see the effect of the rugosity. I have used the same type of elements in the mesh, however I am not achieving the same level of convergence. I am using k-epsilon model. Does anyone have a suggestion in order to get the same level of convergence?

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Old   October 12, 2010, 05:18
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Sorry for the mistake. The correct post is:

Hi all.

I am simulating a free surface flow where the bed is hydraulically rough (several triangles equally spaced). I have already achieved convergence (1o^-5 of residual and 0.01 of imbalance) for a case test where the
height of the triangles is very small ( I have used the multi grid solver in expert parameter).

Now I am trying to increase the height of the triangles, the height of the water and the height of the domain to see the effect of the rugosity. I have used the same type of elements in the mesh, however I am not achieving the same level of convergence. I am using k-epsilon model. Does anyone have a suggestion in order to get the same level of convergence?

Best Regards
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Old   October 12, 2010, 18:13
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Glenn Horrocks
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Why are you using the multi-grid solver expert parameter? CFX uses a multi-grid solver by default anyway and you should not change the defaults unless you have a good reason to do so.

What do you mean by rugosity? Is your simulation steady or transient?

It could be that increasing the size of the triangles is generating new flow features which your current solver settings are having problems resolving. Have you looked here: http://www.cfd-online.com/Wiki/Ansys...gence_criteria
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Old   October 12, 2010, 22:33
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Michael P. Owen
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Have you post-processed the residuals to determine where and why they are high?
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