Steady or Transient

noobies · February 17, 2012, 10:08

Hi everybody
I am trying to obtain Cl and Cd for my half wing 3d simulation and also want to see a wingtip vortex core but when i run the simulation, first i choose steady state for simulation but my solution is not convergence the continuity residual is going around e-1 and then oscillation around some point(other residual is around e-6). Now i change to transient simulation this time the continuity residual is going to e-6 (same boundary condition with steady). Is the value from transient simulation correct? and Which one should i choose Steady or Transient?
If Steady, Do i have to re-mesh (because of my continuity residual is too high)?

My object is to obtain lift curve slope and drag curve slope of the wing
and see wingtip vortex at position behind the wing

thanks

m9819348 · February 17, 2012, 14:38

Hi,

That is a good question.

From a physical point of view, I'd say your problem is a transient one (hence the residual situation).

That does not mean you can not get useful answers using steady state! It is faster and sometimes even more accurate (depending on turbulence model used etc).

In the industry, I have seen both approaches being used successfully. It realty depends what you want exactly. Don't forget that CFD is the tool, not the goal. You are the engineer/scientist! You decide.

Ries Bouwman

February 17, 2012, 10:08	Steady or Transient	#1
noobies New Member Chanchai Join Date: Jan 2012 Posts: 1 Rep Power: 0	Hi everybody I am trying to obtain Cl and Cd for my half wing 3d simulation and also want to see a wingtip vortex core but when i run the simulation, first i choose steady state for simulation but my solution is not convergence the continuity residual is going around e-1 and then oscillation around some point(other residual is around e-6). Now i change to transient simulation this time the continuity residual is going to e-6 (same boundary condition with steady). Is the value from transient simulation correct? and Which one should i choose Steady or Transient? If Steady, Do i have to re-mesh (because of my continuity residual is too high)? My object is to obtain lift curve slope and drag curve slope of the wing and see wingtip vortex at position behind the wing thanks

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February 17, 2012, 14:38		#2
m9819348 New Member Ries Bouwman Join Date: Mar 2009 Location: Graz, Austria Posts: 28 Rep Power: 17	Hi, That is a good question. From a physical point of view, I'd say your problem is a transient one (hence the residual situation). That does not mean you can not get useful answers using steady state! It is faster and sometimes even more accurate (depending on turbulence model used etc). In the industry, I have seen both approaches being used successfully. It realty depends what you want exactly. Don't forget that CFD is the tool, not the goal. You are the engineer/scientist! You decide. Ries Bouwman