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Incorrect formula for supersonic total pressure calculation

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Old   September 21, 2021, 07:51
Default Incorrect formula for supersonic total pressure calculation
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Sai Darbha
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The static pressure for the totalPressure boundary condition for compressible, supersonic flow in OpenFoam-v2012 is given in doxygen and the code as:

P_s = \frac{P_T}{\left( 1 + \psi \left( \frac{\gamma -1}{2 \gamma} \right) |\vec{u}|^2 \right)^{\gamma / (\gamma -1)}}

where the compressibility, psi is related to the speed of sound, c as

\psi = \frac{1}{c^2}


However, the isentropic relation for supersonic flows relate the static pressure to stagnation pressure as:

P_s = \frac{P_T}{\left( 1 + \psi \left( \frac{\gamma -1}{2 } \right) |\vec{u}|^2 \right)^{\gamma / (\gamma -1)}}

For reference, have a look at: https://www.grc.nasa.gov/www/k-12/ai.../isentrop.html


Is this a bug or am I missing something? Please suggest.

Thanks,
Sai
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