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-   -   Why's FLUENT changing the reference values? (http://www.cfd-online.com/Forums/fluent/49724-whys-fluent-changing-reference-values.html)

siw November 6, 2008 14:17

Why's FLUENT changing the reference values?
 
Hi,

I'm running 5 oblique shock and 5 expansion wave simulations all with upstream conditions: Mach = 3.7, pressure = 101325Pa and temperature = 288.15K. All ideal gas so Cp = 1006.43J/kg K selected from in Fluent.

Why is it that when I go to both the Initialze and Reference boxes these values are slightly changed and that the changes are different for the 10 simulations? I have gone through the input files very carefully to make sure that all settings are the same.

For example. In one oblique shock case the Initialize box says pressure = 101325.2Pa, velocity x-comp = 1258.607m/s and temperature = 288.1501K. Where did FLUENT get these 0.2 and 0.0001 from? For the same case the Reference box has the same values with density = 1.225066kg/m^3 and enthalpy = 1082049J/kg. Since I'm using the Standard atmosphere in the inputs the density should be 1.225kg/m^3.

For any other example these small changes are slightly different again, so there's no consistancy.

I know these are small changes but I want know why FLUENT does this. I have noticed from the outputs that these small differences grow making final comparsions of the 10 solutions less valid.

If FLUENT is doing this for a reason then these small amounts must be exactly the same for all 10 simulations. It certainly doesn't help build confidence in using the package.

If I don't get any help in the next few days I'll just have to submit my college report explaining this FLUENT inconsistancy.

Thanks.



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