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Old   May 8, 2014, 10:05
Default Transient RANS Simulation
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Hello,

to this point I have only worked with steady state RANS Simulation. I have found a thesis where a transient RANS Simulation was described including animations over time.

As far as I understood the RANS Simulation will give us averaged values so the animation for a transient RANS Simulation doesn't make sense to me. Am I correct in assuming that it just shows physical nonsense till the mean values do not vary anymore (respectively the residual target are met) and afterwards the animation will not change anymore?

Thanks for your help!
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Old   May 8, 2014, 12:09
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Quote:
Originally Posted by Bazinga View Post
Hello,

to this point I have only worked with steady state RANS Simulation. I have found a thesis where a transient RANS Simulation was described including animations over time.

As far as I understood the RANS Simulation will give us averaged values so the animation for a transient RANS Simulation doesn't make sense to me. Am I correct in assuming that it just shows physical nonsense till the mean values do not vary anymore (respectively the residual target are met) and afterwards the animation will not change anymore?

Thanks for your help!

Think about the compression/expansion flow cycle in an engine chamber. At each time (or crank angle), the URANS provides the solution that has the meaning of representing an "ensemble average" of N solutions at that time.
The animation does not represent the real physics you would observe in an experiment (or in DNS).
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Old   May 8, 2014, 13:14
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Thank you very much for your reply!

So what the URANS does is it gives me an average solution for every crank angle. I get the idea for a changing geometry like in an engine chamber.

But, when I have a geometry that isn't changing - let's say a flow over a cube - there is no reason to use a URANS.

Am I correct in my thinking?

Thanks again for you help
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Old   May 8, 2014, 14:37
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the URANS is based on a particular decomposition, the averaged field is time dependent in terms of external forcing frequency (as in the engine) or low frequency as vortex shedding behind a bluff body where the main frequency can be identified. Again, the animation does not represent a point-wise time-evolution of the flow
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