# Dimension of pressure: M/LT2 or L2/T2?

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 August 7, 2013, 13:57 Dimension of pressure: M/LT2 or L2/T2? #1 New Member   gcengineer Join Date: Oct 2012 Posts: 23 Rep Power: 4 Sometimes the dimension of pressure is specified differently in 0/p file for different problems: tutorials/basic/potentialFoam/cylinder dimensions [0 2 -2 0 0 0 0]; tutorials/compressible/rhoSimpleFoam/angledDuctExplicitFixedCoeff dimensions [1 -1 -2 0 0 0 0]; What tips me off to the correct dimension to use for a particular problem? Is there a general rule for the correct dimension of pressure in 0/p file? Is it simply a matter of whether the problem is 2D or 3D? Compressible or incompressible? I see that (M/LT2)/(M/L3) = L2/T2. Thanks. Last edited by gcengineer; August 7, 2013 at 13:59. Reason: Courtesy

 August 7, 2013, 15:37 #2 Senior Member   Nima Sam Join Date: Sep 2009 Location: Tehran, Iran Posts: 1,123 Blog Entries: 1 Rep Power: 14 one is pressure and the other one is pressure divide on density __________________ Training Course on OpenFOAM at (http://www.isme.ir/) My Weblog (http://openfoam.blogfa.com/)

 August 7, 2013, 15:44 #3 New Member   gcengineer Join Date: Oct 2012 Posts: 23 Rep Power: 4 Thank you, nimasam, for responding. As I wrote, "I see that (M/LT2)/(M/L3) = L2/T2." What I want to know is why does one case require M/LT2, but another requires L2/T2? Is it 2D v 3D? Compressible v incompressible? Choice of solver? Last edited by gcengineer; August 7, 2013 at 15:45. Reason: Correction

 August 7, 2013, 15:59 #4 Senior Member   Nima Sam Join Date: Sep 2009 Location: Tehran, Iran Posts: 1,123 Blog Entries: 1 Rep Power: 14 you should check each solver , but its pressure on density in some incompressible solvers __________________ Training Course on OpenFOAM at (http://www.isme.ir/) My Weblog (http://openfoam.blogfa.com/)

 August 7, 2013, 16:24 #5 New Member   gcengineer Join Date: Oct 2012 Posts: 23 Rep Power: 4 It appears that the dimension of pressure is M/LT2 for compressible solvers and L2/T2 for incompressible solvers. Here, Boussinesq solvers are incompressible (e.g., buoyantBoussinesqSimpleFoam, buoyantBoussinesqPimpleFoam). If there is an exception to this rule, I would appreciate knowing about it. Thanks.

 August 7, 2013, 16:29 #6 Senior Member   Nima Sam Join Date: Sep 2009 Location: Tehran, Iran Posts: 1,123 Blog Entries: 1 Rep Power: 14 forexample interFoam which is two-phase incompressible solver __________________ Training Course on OpenFOAM at (http://www.isme.ir/) My Weblog (http://openfoam.blogfa.com/)

 August 7, 2013, 16:41 #7 New Member   gcengineer Join Date: Oct 2012 Posts: 23 Rep Power: 4 Yes. However, for the cases in /tutorials/multiphase/interFoam, there is no 0/p, but 0/p_rgh has dimension M/LT2. Thanks again.

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