# icoFoam - high number of iterations for pressure field computation

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

 April 23, 2013, 09:48 icoFoam - high number of iterations for pressure field computation #1 Senior Member   Join Date: Nov 2012 Location: Bavaria Posts: 145 Rep Power: 6 Dear All, I ran an icoFoam job. Geometry: flow channel (L=3100mm, B=250mm, H=20mm). Like in the cavity tutorial case I've defined a moving top. icoFoam case 1: kinematic viscosity newtonian fluid icoFoam case2: kinematic viscosity newtonian fluid total simulation time = 2s Unfortunately I didn't log the simulation progress. According to the couple of last iteration steps print on the screen there is a tremendously high number of iterations for the pressure field computation in case 2 whereas in case 1 the number of iterations for pressure (just as for velocity) is in the beginning of the computation small and finally zero. I read following thread: http://www.cfd-online.com/Forums/ope...-pressure.html I've tried to understand chapter seven (Ferziger, Peric) about pressure correction but am still too much of a beginner to be in the know. I would like to understand the high number of iteration steps for pressure field in case 2. Can anybody help? Aylalisa

 April 23, 2013, 11:02 #2 Senior Member   HECKMANN Frédéric Join Date: Jul 2010 Posts: 237 Rep Power: 10 Just for curiosity, what is the pressure gradient in your second case ? How much is the inlet and outlet in your final solution ? I don't know how is icoFoam but some other solver have troubles if the pressure gradient is too small. Try to change your scheme maybe.

April 24, 2013, 07:14
#3
Senior Member

Join Date: Nov 2012
Location: Bavaria
Posts: 145
Rep Power: 6
Hi Fredo,

Quote:
 Originally Posted by fredo490 Just for curiosity, what is the pressure gradient in your second case ? How much is the inlet and outlet in your final solution ? I don't know how is icoFoam but some other solver have troubles if the pressure gradient is too small. Try to change your scheme maybe.
I've only a moving top that should produce the flow. That is at least what I wanted to try out to get a feeling for icoFoam (and its weakness, if existing).
I've defined Inlet and outlet as walls. It's not for example like in an extruder where you get a flow produced by a given p and a moving wall (extruder screw).

Did I maybe misinterpret your question?

Aylalisa

 April 24, 2013, 08:21 #4 Senior Member   HECKMANN Frédéric Join Date: Jul 2010 Posts: 237 Rep Power: 10 Try to plot the resituals to check what happen during your computation: http://www.cfd-online.com/Forums/ope...residuals.html aylalisa likes this.

 May 15, 2013, 12:29 Plotting Residuals #5 Senior Member   Join Date: Nov 2012 Location: Bavaria Posts: 145 Rep Power: 6 Hi, I've followed instructions of the 'how to plot residual' thread: http://www.cfd-online.com/Forums/ope...residuals.html The icoFoam computation runs. The residuals of Ux, Uy, Uz and p have been plot. simulation time: 3s, delta t : 0,002s Plot of first run (simulation time: 2s, delta t: 0.002s): Question 1: Why stops the residual plot of Ux and Uz after about 150 iterations? The simulation momentarily runs and the script 'Residual.txt' supplies, each time it is called, following message on the screen: 'warming: Skipping data file with no valid points' Does that message have something to do with the fact the curves of Ux and Uz have already stopped beeing plot??? Have Ux and Uz already been converged? Question 2: Another fact, according to the entries in controlDict, confuses me: endTime 3s deltaT 0.002s writeControl timeStep writeInterval 2 Since I've set writeInterval to 2 I've expected that entries in the log file will be written after 2 timeSteps. But there is an entry for each timeStep in the log file. What does 'writeControl timeStep' actually mean? Question 3: Has the fact, that pressure computations needs about 1000 iterations per time step, something to do with the pressure correction method used in icoFoam? Thanks for each reply! Aylalisa

 July 9, 2014, 08:59 #6 New Member   Join Date: Nov 2012 Posts: 27 Rep Power: 6 Hi aylalisa, did u find the answer of high iteration number? I am doing DNS of turbulent pipe flow. I am facing also the same problem.

 July 21, 2014, 04:20 #7 Senior Member   T Chourushi Join Date: Jul 2009 Posts: 321 Blog Entries: 1 Rep Power: 11 Can you post your "controlDict", "fvsolution" & "fvschemes" files here? Check with reduced deltaT. -- Best Luck!

 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 Niklas Wikstrom (Wikstrom) OpenFOAM Running, Solving & CFD 122 June 15, 2014 06:20 sivakumar OpenFOAM Running, Solving & CFD 7 March 17, 2013 07:37 nileshjrane OpenFOAM Running, Solving & CFD 4 February 25, 2013 05:13 Alan OpenFOAM Running, Solving & CFD 10 April 6, 2012 14:02 sunnysun OpenFOAM Running, Solving & CFD 5 March 16, 2009 04:32

All times are GMT -4. The time now is 11:10.