# why totalPressure formulas are different?

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 April 10, 2013, 19:48 why totalPressure formulas are different? #1 Senior Member     Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,209 Rep Power: 20 in header file of totalPressure in 2.2.0 version its explained briefly about categories of totalPressure bc. Why for subsonic compressible flow we should use p0=p+.5*rho*U^2 and not the isentropic equation that includes mach in it like in gas dynamics texts?

 April 11, 2013, 04:41 #2 Senior Member     Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,209 Rep Power: 20 whats the reason of choosing different formula in subsonic and supersonic for compressible flow?

 April 11, 2013, 08:37 #3 Senior Member     Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,209 Rep Power: 20 it is what has been written in totalPressureFvPatchField.H Code: The modes of operation are set via the combination of \c phi, \c rho, and \c psi entries: \table Mode | phi | rho | psi incompressible subsonic | phi | none | none compressible subsonic | phi | rho | none compressible transonic | phi | none | psi compressible supersonic | phi | none | psi \endtable and: Code: compressible subsonic: \f[ p_T = p_0 + 0.5 \rho |U|^2 \f] where \vartable p_T | total pressure [Pa] p_0 | reference pressure [Pa] \rho | density [kg/m3] U | velocity \endvartable while in all educational texts I have seen that this relation is for incompressible flow and for compressible flow we should use isentropic relations. could anyone help me with this doubt on the concept?

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