
[Sponsors] 
July 9, 2007, 09:13 
steady state solution

#1 
Guest
Posts: n/a

Hi,
Does steady state solution depends on your initial guess? cfxdude 

July 9, 2007, 09:35 
Re: steady state solution

#2 
Guest
Posts: n/a

A complete converged solution (i.e. constant values in monitoring points, imbalances=0, RMS residuals < 1e6) should not depend on initial guess.
GertJan 

July 9, 2007, 09:57 
Re: steady state solution

#3 
Guest
Posts: n/a

Hi,
What you are saying is that If 1e5 < RMS residuals (pressure and velocities) <1e4 and 1e6 < RMS residual (ke turb) < 1e3 is not a steady state solution, or the solution depends on the initial guess? In my case the velocity of the monitored point is fluctuating between 0.25  0.35 m/s (11000 iteration), but the volume average velocity is constant. which one is the correct steady state indication. Thanks. cfxdude 

July 9, 2007, 10:31 
Re: steady state solution

#4 
Guest
Posts: n/a

When your monitoring values are fluctuating, you won't have a steady state situation. Looks like your problem is time dependent.
GertJan 

July 9, 2007, 10:38 
Re: steady state solution

#5 
Guest
Posts: n/a

So constant volume average velocity is not the steady state indication.
Is there any book or paper about these, I am looking for some thing written. Thanks for your time. A.A. 

July 9, 2007, 18:20 
Re: steady state solution

#6 
Guest
Posts: n/a

Hi,
For a small number of situations the steady state solution does depend on the initial guess. I have seen some flows were the Coanda effect caused a jet to stick to one wall or the other depending, then settle down to a steady state solution. Which wall the jet stuck to depended on the initial guess. In general, however, a fully converged solution is independent of initial guess. Glenn Horrocks 

July 9, 2007, 18:28 
Re: steady state solution

#7 
Guest
Posts: n/a

If the velocity of the monitored point is fluctuating between 0.25  0.35 m/s after 11000 iteration, try to increase gradually the timescale. In this way you should obtain a non fluctuating velocity value.
Probably now you are reading some fluctuations of your domain; increasing the timescale works as a filter for this numerical fluctuations. Bye Alberto 

July 10, 2007, 05:43 
Re: steady state solution

#8 
Guest
Posts: n/a

Numerical fluctuations? You may damp out physical fluctuations by numerics. If you increase the time step you may stabilize the solution but you will not get a fully converged (grid independant and time step independant) solution.
I agree with GertJan and Glenn 

Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Steady State Vs Transient answers  Kushagra  CFX  19  September 22, 2016 18:46 
Solver for transonic flow?  Martin Hegedus  OpenFOAM Running, Solving & CFD  22  December 16, 2015 05:59 
mass flow in is not equal to mass flow out  saii  CFX  2  September 18, 2009 08:07 
Steady State 2 phase problem  fivos  FLUENT  0  April 27, 2009 16:34 
regarding steady state discrete phase calculations  hajszan_gyula  FLUENT  1  February 28, 2006 02:32 