CFD Online Logo CFD Online URL
Home > Forums > FLUENT

Unsteady solution

Register Blogs Members List Search Today's Posts Mark Forums Read

LinkBack Thread Tools Display Modes
Old   August 11, 2006, 11:13
Default Unsteady solution
Posts: n/a
Hi everybody,

I am currently doing an internship and i have a very simple problem to solve. So easy that i am not able to solve it alone...

I ll try to discribe as best i can my 3d pb: It is a disc (hollow cylinder) of fluid. I modeled only 4degrees to solve faster. The top and the bottom are 2 walls. The left and right are 2 periodics walls. The small cylinder is the inlet flow and the big cylinder is the outlet. The inlet is defined by the flow rate and a direction that i change.

I tried different angles for my inlet flow and i have different shape of flow. For angles the solution do not converge and i think that there is unsteadiness. I tried to solve with unsteady model but i have no idea to how parameter the iteration. I tried lot of different way.

I find one result where the residuals move periodicaly, and the shape of velocity seems to be correct to me. But when i keep the same parameters exept the nb of iteration per time step (from 60 to 350) the solution changes. Is this signify that my first solution was wrong? What the residuals are doing when the solution is converged for an unsteady flow? Is there a real solution because of the flow is always changing? how to get it?

The only thing i understand is that time step is very important because you can miss unstable mouvement if its too big or too small. But what is the effect of number of iteration per time step?

If my explaination is not clear, ask me, i ll do my best, as french as i am, to explain it better.

Thanks for any help.


  Reply With Quote


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
Oscillating Cylinder in Parallel Flow: Analytical Solution startingcfd Main CFD Forum 7 March 23, 2012 06:49
How to get the solution of last time step? lzgwhy Fluent UDF and Scheme Programming 0 September 15, 2010 22:23
residual plot after solution reset plaunie STAR-CCM+ 1 April 3, 2010 06:53
Does FOAM converge to exact solution in Laplace equation? santiagomarquezd OpenFOAM Running, Solving & CFD 0 March 26, 2010 08:52
UDF solution variable for time-averaged mass frac? A. S. FLUENT 0 May 14, 2007 16:44

All times are GMT -4. The time now is 13:00.