# why residual of contiunity increases steeply

 User Name Remember Me Password
 Register Blogs Members List Search Today's Posts Mark Forums Read

 July 20, 2003, 20:24 why residual of contiunity increases steeply #1 Anna Guest   Posts: n/a Hello FLUENT user, In my modelling, the setting conditions are unsteady, laminar flow; I actived energy because I need different working temperatues; two phases air-oil; atomsphric pressure. A simple model but iteration couldn't finish. Residuals increased dramatically then simulation stop. Anybody can tell me what is the problem in my setting? Many thanks in advance. Anna

 July 22, 2003, 06:06 Re: why residual of contiunity increases steeply #2 mateus Guest   Posts: n/a Hi! Try to use the standard approach to the problem of convergence... - Decrease underrelaxation (not under 0.2 or 0.3 - the solution will become unphisical) - try to approach the operating point in a few steps (increase velocity fom 0 to operating velocity) - try to solve steady and then use the solution as initial solution for unsteady - decrease time step (courant number if you are using VoF) -chech the past messages on forum (there has been a lot of discusions on this topic) Good luck MATEUS

 July 22, 2003, 17:37 Re: why residual of contiunity increases steeply #3 James Date Guest   Posts: n/a This could be any manner of things: 1) Poor grid quality, i.e. high aspect ratio cells, cells with very high skew & rapid changes in cell size. 2) Specifying incorrect / non realistic initial boundary conditions and or physical properties. 3) Too high under-relaxation factors. 4) Differencing Scheme issues, i.e. false diffusion. 5) If you're using a near wall (Wall Function turbulence model i.e. K-e) make sure the Y+ is in the correct range. i.e. 30 < Y+ < 500. With 11.63 as an absolute minimum. 6) Trying to solve an unsteady / time dependant problem using a steady state solution method. 7) Using too large a time step when carrying out transient computations. 8) Positioning boundaries (especially outflow boundaries) too close to regions with high flow gradients / recirculation regions. 9) Pressure correction issues. The list goes on! All the best in obtaining a converged solution, time and patience and you'll track the problem down. Regards James

 July 22, 2003, 22:06 Re: why residual of contiunity increases steeply #4 alex Guest   Posts: n/a Hi I just want to tell you that even though you obtained divergence check the properties contours and x-y plots. In other words learn from your case where the flow is giving you unexpected results. New CFD users tend to play with the computational parameters too much, without looking a previous analysis of the results. I sugguest that you save the results until the point where the simmulation was convergence and then after 50 or 100 iterations. This approach will provide enough information to tell you if you have a periodic flow. Best regards Alex Munoz

 July 22, 2003, 22:41 Re: why residual of contiunity increases steeply #5 Anna Guest   Posts: n/a Hi thank you guys very helpful suggestions.

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post Lord Kelvin OpenFOAM Running, Solving & CFD 8 March 28, 2016 11:08 xiuying OpenFOAM Running, Solving & CFD 8 August 27, 2013 15:33 jonmec OpenFOAM Running, Solving & CFD 3 July 28, 2011 05:24 carsten OpenFOAM Bugs 11 September 12, 2008 11:16 sivakumar OpenFOAM Pre-Processing 9 September 9, 2008 12:53

All times are GMT -4. The time now is 03:00.

 Contact Us - CFD Online - Privacy Statement - Top