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-   -   Steady vs. Transient (https://www.cfd-online.com/Forums/fluent/96054-steady-vs-transient.html)

egge24 January 11, 2012 08:24
Steady vs. Transient
 
Hi,

I'm modeling an explicit porous disk inside a water tank. I run a steady and transient simulations, with the only difference between them is the scheme used for each simulation, SIMPLEC for steady and PISO for transient.

Results are very different!! See figures. The wake region in the transient simulation is way shorter tan for the steady simulation.

Does anybody know THE WHY of this disagreement??

http://img33.imageshack.us/img33/589...lsteadycon.jpg
Fig-1: Steady simulation.


http://img209.imageshack.us/img209/6...ltransient.jpg
FFig-2: Transient simulation.

Rhyno466 January 11, 2012 14:03
It is my understanding that the transient case gives more of an instantaneous solution at a given time and the steady solution is given as a time averages one.

egge24 January 11, 2012 20:36
Rhyno466,

I think the problem was that I didn't run the transient simulation for enough time. I did so, and wake length for the transient simulation is getting similar to the steady case.

LuckyTran January 13, 2012 23:49
Quote:
Originally Posted by egge24 (Post 338923)
Rhyno466,

I think the problem was that I didn't run the transient simulation for enough time. I did so, and wake length for the transient simulation is getting similar to the steady case.
There should not be any differences between a steady and transient simulation if all else (boundary conditions, models) are the same. Since more things are likely to go wrong in a transient simulation than a steady one, most likely your transient simulation was not run properly. Keep trying.


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