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Difference steady state / unsteady

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Old   March 4, 2024, 15:15
Smile Difference steady state / unsteady
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Daniel
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Hei, im getting used to work with openFoam but Im having a hard time understanding the difference between steady state solver like simple and unsteady like pimple/piso. a Flow is called steady state when it doesn't change over time. However I found a YouTube tutorial where simple is used vor a vortex shed problem (https://www.youtube.com/watch?v=Udt3...ist=WL&index=1)
The same problem is listed in tutorials -> incompressible -> PimpleFoam->LES->Vortexshed ) The results look nearly the same.

I don't understand in general what openFoam writes as solution. Like in Simple you have to insert a Time-Step but this is the Step for the iterations of the solving process. So each step the solution gets more precise and your only interested in the last solution (in best case it converges before the last iteration step) bc this is the most precise solution for your case? Or where do is see time steps as "real" time? Like in unsteady state solutions.
Are the solution which get exported solution which represent real time steps and then you see the solution develop over time or are these just iteration that get more precise over time and only the last on is the best solution?

However in unsteady solver - are these written solution time steps or also just the iterations and the higher the number of the written solution the more precise it is?

Im just wondering because I wanna visualize how a vortex like in vortex shed behaves over time. How its moves, maybe it splits or it just dissipates.

How can this be done? I came across the word transient simulation, but is transient not equal to unsteady state?


Why is it possible in an unsteady solver to visualize the flow over time, like how it porpergates through the domain. Wen uniformfield is (0 0 0) and inlet boundary condition is for example (5 0 0) the velocity needs some time to hit an object (if the mesh is big enough)- but the solution is always a given field which has already been fully developed. How can I see how the flow develops over time?

And what is an example for steady state and unsteady? I always thought turbulence is an unsteady event. But why can you solve it then with steady state solver?

Im confused af
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Old   March 9, 2024, 09:25
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Shravan
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For future reference, please check out this thread: Difference steady state / unsteady
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