# pressure unit ? boundary condition

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 October 28, 2009, 04:52 pressure unit ? boundary condition #1 Senior Member   Jiang Join Date: Oct 2009 Location: Japan Posts: 186 Rep Power: 11 Dear Foamers, I am confused about pressure unit. in SI unit ,should use Pascals, that's kg/(m*s2). and so [1 -1 -2 0 0 0 0]. why openfoam use like this in many tutorials: dimensions [0 2 -2 0 0 0 0]; internalField uniform 0; for pressure boundary conditions ,we should use real pressure? for example: 101325 Pa. Thank you. vinayvm and peaceout like this.

 October 28, 2009, 05:43 #2 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,290 Rep Power: 36 OpenFOAM uses the rho-normalized pressure p*=p/rho [p*] = {kg/(m.s**2)} /(kg/m**3) = m**2/s**2 = [0 2 -2 0 0 0 0] in your BC you just have to divide your real pressure with your density anothr_acc, sina_mech, Atze and 11 others like this. __________________ In memory of my friend Hervé: CFD engineer & freerider

October 28, 2009, 07:14
#3
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Jiang
Join Date: Oct 2009
Location: Japan
Posts: 186
Rep Power: 11
Quote:
 Originally Posted by -mAx- OpenFOAM uses the rho-normalized pressure p*=p/rho [p*] = {kg/(m.s**2)} /(kg/m**3) = m**2/s**2 = [0 2 -2 0 0 0 0] in your BC you just have to divide your real pressure with your density
Thank you very much, mAx
I understand.

December 29, 2013, 18:21
#4
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Ke Wu
Join Date: Jan 2012
Posts: 185
Rep Power: 9
Quote:
 Originally Posted by -mAx- OpenFOAM uses the rho-normalized pressure p*=p/rho [p*] = {kg/(m.s**2)} /(kg/m**3) = m**2/s**2 = [0 2 -2 0 0 0 0] in your BC you just have to divide your real pressure with your density
How about other unit like velocity

Any normalization applied to those units

Thanks

 January 2, 2014, 04:43 #5 Senior Member   Join Date: Aug 2013 Posts: 361 Rep Power: 8 Hi Ke Wu, Nope. Rest of the variables are generally not normalized by the density. As far as I know only p and p_rgh. If you want to double check, you can always see dimensions for every variable and check if it is the right unit or not. Regards, Antimony

 October 21, 2018, 15:36 #6 New Member   merve Join Date: Jul 2018 Posts: 1 Rep Power: 0 Wall Shear Stress is the same in OpenFOAM.