# why I can only use SIMPLE of 1 order?

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

 May 29, 2002, 04:21 why I can only use SIMPLE of 1 order? #1 quain tchew Guest   Posts: n/a I'm computing a combustion chamber of an engine which has two subsonic air inlets, a fuel inlet and a nozzle. I set 1 the air inlets as pressure inlets with totol pressure of about 950000 Pa; 2 the fuel inlet as mass flow inlet with mass flux of 0.09kg/s; 3 the nozzle as pressure outlet with 26000Pa. I use ideal-gas model, K-E turbulence model with standard wall function. Only with SIMPLE method of one order, I got a converged result. But when I switch to two order simple method, it didn't converge. I don't know why? Any one give some advices?

 May 29, 2002, 04:49 Re: why I can only use SIMPLE of 1 order? #2 Jin-Wook LEE Guest   Posts: n/a It is very natural that 1st order is cheaf(CPU time) and easy to converge and 2nd order is expensive and difficult to converge. Comments : 1. 1st order is easy to converge because of numerical diffusion which has the effect of smoothing the result. 2. To enhance the convergence, there are couple of approaches such as, - good mesh(low skewness) - low under-relaxation - step by step approach(e.g., mixing only --> reaction) - and so on Sincerely, Jinwook

 May 30, 2002, 05:54 Re: why I can only use SIMPLE of 1 order? #3 Quain Tchew Guest   Posts: n/a Thanks I have tried low under-relaxation, but.... Yes, maybe my grid is not good.

 June 3, 2002, 02:34 Re: why I can only use SIMPLE of 1 order? #4 moiami Guest   Posts: n/a Try this: do 1st order then after it is converged carry on the simulation but replace 1st with 2nd (like in the tutorial). You'll see a rise in peak for the residual plot b4 it peters down to a convergence. But b4 that you have to be clear on why you're using 2nd order. You may not have to, you know (see message below: Posted By Gavin Date: Wed, 29 May 2002, 4:12 a.m. in Response To: convergence problems (jeremy))

 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 zouchu Main CFD Forum 1 January 20, 2014 18:02 fisch OpenFOAM Running, Solving & CFD 2 July 6, 2011 04:37 shekharc Main CFD Forum 1 July 23, 2009 13:53 moomba Main CFD Forum 8 May 26, 2009 08:17 saygin Main CFD Forum 2 January 30, 2006 12:45

All times are GMT -4. The time now is 07:35.