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Old   December 9, 2012, 17:32
Default free surface simulation
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I desperately trying to run a free surface simulation of an river section. The Problem is, that I canīt get a nice surface without refinement. I tryed almost everything. For testing I have a simpel rectangular channel with an laminar flow of 10 by 4m (20m long, Hex-mesh 0,4m max). The flow seems fine at the botton but gets turbulent close to the surface. At the Inlet the water close to the surface goes down as you can see in the attachment. At the Outlet it goes up again. Is there a way to get it straigt without refinement of the surface.
I would be thankful for any tip
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File Type: jpg Inlet.jpg (93.5 KB, 43 views)
File Type: jpg Outlet.jpg (68.5 KB, 28 views)
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Old   December 10, 2012, 16:30
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Eva Skarupova
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Could you post your settings here? At least inlet and outlet condition.
Did you checked "Tutorial 9: Free Surface Flow Over a Bump"?

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Old   December 13, 2012, 14:02
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I've been struggling with the same problem. I have not found any complete solutions. Problem seems to be ansys trys to flatten the surface between timesteps across the mesh which causes small waves to propogate across the surface. There really aren't any solutions found in any of the documents. I think its one of those things you have to try to limit its effects, cant get rid of.

Best thing to do is just refine the mesh at the surface.
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Old   December 13, 2012, 17:37
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Glenn Horrocks
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Spurious currents at the free surface is a common problem with free surface simulations. They are very hard to eliminate in a eularian approach. You can minimise them by careful adhustment of the free surface parameters - I can't remember which, try them all and see which ones work, that's how I found this out - but you will not be able to eliminate it.

Alternate free surface approaches such as level set and single phase VOF have the potential of eliminating this problem - but you will need to go to a different CFD code to do that, CFX does not support any other options.
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