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Old   February 23, 2005, 03:35
Default RSM Model.
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Hello ,

I ran the Reynolds Stress Model (RSM)but this msg shows up while iterating.

'turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 4169 cells

reversed flow in 81 faces on outflow 7. turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 9420 cells'

Does anyone know what this mean and what should I do?


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Old   February 23, 2005, 10:00
Default Re: RSM Model.
Chris Bailey
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FWIW I've used this and other models and gotten the "reversed flow" message during iteration, meaning that some boundary I defined as an outlet has to be acting as an inlet over some of its area or length. Often this message has disappeared as the iteration has progressed, because the apparent need for inward flow here is just an artifact of incomplete solution. If the message never disappears, it seems there must be some circulating flow overlapping your boundary, and this won't be modeled nicely because the direction and velocity of air flowing in at this boundary isn't being modeled and you're not specifying it well either. You could move the boundary further out, or change the geometry if you're designing geometry and don't want circulation there.

I also get messages about the limits, but don't understand much about them.
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Old   February 23, 2005, 12:05
Default Re: RSM Model.
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The limits are a set of values that Fluent uses to try to contain the solution to keep it from diverging. You can set them under Solve->Controls->Limits

I HIGHLY recommend doing this!! What happens is that as the model iterates, sometimes it increases pressure (for example) to an extreme value as it tries to work out difficult parts of the flow... to keep the model from diverging, the value is not allowed to exceed what is set in the limits. Then as the model converges, these extremes get worked out... but they ONLY get worked out if your model is setup properly and you have a decent grid. If the Turbulent Viscocity Ratio warning doesn't go away, then it means there's a problem with your grid... cells too large behind a sharp corner... that kind of thing. If the error lasts more than 100-200 iterations, I recommend finding out where the problem is and trying to understand why it's there and what to do about it.

Hope this helps, and goodluck, Jason
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