# 1st order vs 2nd order

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

 LinkBack Thread Tools Display Modes
 April 1, 2005, 21:25 1st order vs 2nd order #1 ken Guest   Posts: n/a Hi I'm simulating flow throught 2 parallel plates with inclined inlet and outlets. I tried the second order upwind momentum discretization (and also QUICK) but it couldn't converge very well. For example the average velocity in a plane was fluctuaing at around 1% of its maximum value. But when I switched to the first order upwind, this fluctuation is reduced to 0.2%. I know first order can converge more easily and 2nd order is more accurate. But will a 2nd order solution that is partially converged be more accurate than a 1st order one? Are there any ways to help the 2nd order solution converge? I have reduced the momemtum under relaxation to 0.3 but to no avail. I was wonder if I should make some changes to the multigrid entries. Any suggestions?

 April 2, 2005, 14:54 Re: 1st order vs 2nd order #2 ap Guest   Posts: n/a Try to increase the pressure under-relaxation factor to 0.6 or so. Also consider a grid refinement. Regards, ap

 April 3, 2005, 15:46 Re: 1st order vs 2nd order #3 ken Guest   Posts: n/a Unfortunately that didn't work. In fact the integral of the pressure in the system is also fluctuating and can't converge.

 April 4, 2005, 03:51 Re: 1st order vs 2nd order #4 Luca Guest   Posts: n/a Check your grid elements. If they are high skewed that could be the possible reason. Luca

 April 4, 2005, 20:55 Re: 1st order vs 2nd order #5 ken Guest   Posts: n/a Some of the elements are indeed skewed but I can't do much about it because of the geometry of the domain. Can I work around this by using skewness correction in SIMPLEC or PISO? If so, what is a common value to try?

 April 4, 2005, 21:34 Re: 1st order vs 2nd order #6 ken Guest   Posts: n/a Just found of that PISO dosen't work. I tried it with and without skewness correctiona and used the QUICK scheme with it.

 April 5, 2005, 03:04 Re: 1st order vs 2nd order #7 Luca Guest   Posts: n/a You should try to correct your grid...I had your same problem and when I remeshed the problem was solved. Luca

 April 6, 2005, 01:23 Re: 1st order vs 2nd order #8 ken Guest   Posts: n/a I remeshed taking care in reducing the number of skewed elements. It dosen't seem to work. As before, the residuals can't get below 1e-3 when I used 2nd order upwind. Pressure is also fluctuating.

 March 14, 2013, 04:43 Van leer second order and AUSM+ #9 New Member   kian Join Date: Feb 2013 Posts: 14 Rep Power: 7 Hi, I've got a fortran code for solving 2D compressible flow over an airfoil with the method of first order van leer flux vector splitting . I have to change it to second order van leer flux vector splitting method . Can you please help me on how to do it? It's also possible for me to solve this project with the method of AUSM+ . Are you familiar with this method? can you help me with it please? Thanks a lot in advance

 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 Far Main CFD Forum 7 March 14, 2013 13:29 fisch OpenFOAM Running, Solving & CFD 2 July 6, 2011 04:37 stevenvanharen OpenFOAM Programming & Development 0 April 11, 2011 05:54 Andrea CFX 2 October 11, 2004 05:12 Prateep Chatterjee FLUENT 0 January 19, 2003 01:31

All times are GMT -4. The time now is 20:28.

 Contact Us - CFD Online - Privacy Statement - Top