# InterFoam performance

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 June 6, 2013, 10:25 InterFoam performance #1 Member   Join Date: Mar 2013 Posts: 98 Rep Power: 13 Hi to all, I have a problem whit the performance of inteFoam. My problem concern a circular pipe filled with liquid and closed to both extremity. At initial time the right wall of the pipe is opened and gas allowing gas to go inside and liquid outside. My aim is to validate OpenFOAM for this kind of problem so I compared its performance with Fluent. The comparison seems very good but there is a strange difference. In my simulations I use a fixed Courant number and adaptive time step. The difference between is that Fluent give me a deltaT around 10e-04 while OpenFOAM give me a deltaT around 10e-6.So the simulation run very slow with OpenFOAM...Why this different behavior?There i a way to speed simulation? I obtain a little accelerate through decreasing tolerance but I would obtain i larger time step if possibile and kwon why there is this difference between two code. thanks to all

 June 13, 2013, 18:04 #2 Senior Member     Join Date: Mar 2013 Location: USA Posts: 120 Rep Power: 13 Giack, You can try to give interFoam a fixed time step. That may help you to speed-up your simulation. Hope this helps, Kilroy

 June 14, 2013, 03:24 #3 Member   Join Date: Mar 2013 Posts: 98 Rep Power: 13 thanks for your reply the problem of using a fixed time step is that I could overcome the maximum Courant number that ensure stability. I find in the forum that a way to run faster is set a maxCoalpha=1 with nAlphaSubCycle=5 (so the maxAlphaCo is 0.2 for each time step of alpha equation) and a maxCo=2. the simulation is a 10% faster but i dont understand the set maxCo=2.interFoam is an explicit solver,so the maxCo have to set to1.I go wrong?

 June 14, 2013, 09:59 #4 Senior Member     Join Date: Mar 2013 Location: USA Posts: 120 Rep Power: 13 I am not an expert on this subject but if your Courant number exceeds the value "1" during an explicit time integration, your simulation will blow up. Maybe your courant number doesn't exceed the value one although you set maxCo=2. Have you tried to run the same simulation by only changing maxCo=1? Maybe it will still be 10% faster. Since your simulation doesn't blow up, I believe that your Courant number is still smaller than 1.

 June 14, 2013, 10:14 #5 Member   Join Date: Mar 2013 Posts: 98 Rep Power: 13 Thanks for the advice,I will test it

 Tags adaptive-time stepping, interfoam, performance, time step