Steady vs. Transient

egge24 · January 11, 2012, 09:24

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??

Fig-1: Steady simulation.

FFig-2: Transient simulation.

Rhyno466 · January 11, 2012, 15:03

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, 21:36

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 14, 2012, 00:49

Quote:

Originally Posted by egge24

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.

January 11, 2012, 09:24	Steady vs. Transient	#1
egge24 Member Join Date: Jan 2011 Posts: 45 Rep Power: 15	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?? Fig-1: Steady simulation. FFig-2: Transient simulation.

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January 11, 2012, 15:03		#2
Rhyno466 Member Ryne Join Date: Jan 2010 Posts: 32 Rep Power: 16	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.

January 11, 2012, 21:36		#3
egge24 Member Join Date: Jan 2011 Posts: 45 Rep Power: 15	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.