# Transient RANS Simulation

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 May 8, 2014, 10:05 Transient RANS Simulation #1 Member   Join Date: Jun 2012 Posts: 94 Rep Power: 6 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!

May 8, 2014, 12:09
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Filippo Maria Denaro
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Quote:
 Originally Posted by Bazinga 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).

 May 8, 2014, 13:14 #3 Member   Join Date: Jun 2012 Posts: 94 Rep Power: 6 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

 May 8, 2014, 14:37 #4 Senior Member   Filippo Maria Denaro Join Date: Jul 2010 Posts: 2,498 Rep Power: 31 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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