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RubenG June 22, 2009 11:09

exact face values

I'm trying to calculate the exact numerical values of the thermodynamic properties (entropy, enthalpy, mass flow, velocity) on the cell faces. With 'exact' I mean the values which are used by Fluent to solve the navier stokes and turbulence equations.

The reason why I do this, is to perform an exergy analysis. I would like to be able to calculate/visualise the irreversibilities in each cell of the computational domain. To obtain these irreversibilities I need to calculate the flow exergy, which is based on the thermodynamic properties of the fluid on the cell faces.

Thusfar I tried to get these values by means of:
- Applying discretization schemes (first order upwind, second order upwind and central differencing scheme)
After setting the 'right' discretization scheme in the solver, I exported the cell center values to Matlab and tried to reconstruct the cell face values by applying the methods described in the paragraph discretization (Fluent manual).
- Drawing a straight line through the cell
The cell face centers are the intersection points of the line with the cell boundaries. These intersection points can be exported to Matlab.

Unfortunately these methods resulted in negative irreversibilities, which are of course non existing. After that I tried to reconstruct the mass imbalances in Matlab, by exporting and applying the same methods to the cell center values. But that resulted to in large deviations from the values which are displayed when Fluent plots the mass imbalances.

Has anyone an idea how I can obtain the exact cell face values from the cell center values?


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