SYMPTOM:
When visualising the variables Isothermal Compressibility and Isentropic Compressibilty in CFX Post, the units and values are not what is expected.
PROBLEM:
The standard text book definitions of these quantities are:
Isothermal Compressibility = -(1/rho)*(drho/dp)_T
Isentropic Compressibility = -(1/rho)*(drho/dp)_s
where _T and _s denote constant Temperature and Entropy respectively. However, in CFX, these variables are defined as follows:
Isothermal Compressibility = (drho/dp)_T
Isentropic Compressibility = (drho/dp)_s
Thus both quantities in CFX will differ from the standard definitions by a factor of -(1/rho).
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WORKAROUND: For visualisation purposes, create new scalar User Variables in CFX Post using the above formulae. For use in the CFX Solver, create new scalar Algebraic Additional Variables in CFX Pre using the above formulae. FIXED IN: Release 11.0. |
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