Steady VS Unsteady

starccm · February 14, 2020, 19:27

Hello

So I did a simulation with steady model of a laminar forced convection flow with
Segregated flow, Steady

But when I'm trying to get same result with unsteady models like coupled flow (or segregated), implicit , .... the result is totally different. You should be able to get same result. Like if the boundary conditions are not changing, same results should be obtained over time and you should reach to the steady state.

where is the problem??!!!

me3840 · February 15, 2020, 19:19

Are you performing temporal averaging and comparing that field to the steady result?

The results will not be identical, in any case.

starccm · February 15, 2020, 21:12

I am not doing any averaging on the data. But even doing averaging shouldn't change anything since the flow is steady.

The results should be the same since the flow is steady. If you use an unsteady model for a steady flow, as the time goes on, the steady state should be reached.

me3840 · February 15, 2020, 23:25

Is the unsteady case producing an unsteady result?

You could make it more steady-like by increasing the timestep a lot.

starccm · February 16, 2020, 00:17

It's weird. After couple of time steps, the solution is not changing.
Definitely it's not the steady state because it is different with the result obtained by steady model.

LuckyTran · February 17, 2020, 13:37

Is the steady case even producing a steady result? Most of the time, it doesn't.

Regardless, I wouldn't expect always the same result. They can be different.

February 14, 2020, 19:27	Steady VS Unsteady	#1
starccm New Member Join Date: Jan 2020 Posts: 13 Rep Power: 6	Hello So I did a simulation with steady model of a laminar forced convection flow with Segregated flow, Steady But when I'm trying to get same result with unsteady models like coupled flow (or segregated), implicit , .... the result is totally different. You should be able to get same result. Like if the boundary conditions are not changing, same results should be obtained over time and you should reach to the steady state. where is the problem??!!!

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February 15, 2020, 19:19		#2
me3840 Senior Member Join Date: Nov 2010 Location: USA Posts: 1,232 Rep Power: 24	Are you performing temporal averaging and comparing that field to the steady result? The results will not be identical, in any case.

February 15, 2020, 21:12		#3
starccm New Member Join Date: Jan 2020 Posts: 13 Rep Power: 6	I am not doing any averaging on the data. But even doing averaging shouldn't change anything since the flow is steady. The results should be the same since the flow is steady. If you use an unsteady model for a steady flow, as the time goes on, the steady state should be reached.

February 15, 2020, 23:25		#4
me3840 Senior Member Join Date: Nov 2010 Location: USA Posts: 1,232 Rep Power: 24	Is the unsteady case producing an unsteady result? You could make it more steady-like by increasing the timestep a lot.

February 16, 2020, 00:17		#5
starccm New Member Join Date: Jan 2020 Posts: 13 Rep Power: 6	It's weird. After couple of time steps, the solution is not changing. Definitely it's not the steady state because it is different with the result obtained by steady model.

February 17, 2020, 13:37		#6
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,672 Rep Power: 65	Is the steady case even producing a steady result? Most of the time, it doesn't. Regardless, I wouldn't expect always the same result. They can be different.