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Reference pressure for Drag/Cd reports?

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Old   May 18, 2017, 15:27
Default Reference pressure for Drag/Cd reports?
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Jake
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Hi,

I'm running simulations on a vehicle and have generated reports for drag coefficient and drag. My question is in the report, what vales should you enter for reference; pressure, density and velocity.

Currently I have reference velocity as the inlet speed (70mph) density as 1.225kg/m^3 and pressure as 101325 Pa but I've been told by someone I work with to use 0Pa as the reference pressure for both reports but this doesn't seem right to me?

Thanks and advance for any help

Jake
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Old   May 18, 2017, 20:36
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These are reference values. There are no right or wrong answers on what you should enter, they're conventions. Most vehicle-based analyses will use the freestream velocity and density as references.

The reference pressure on the report only matters in certain situations (you should look at the user guide to find out which and why!).

The actual value is gauge pressure from the simulation's reference pressure, so 0 Pa is fine.
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Old   January 25, 2018, 10:40
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Out of curiosity: if I'd like to create a report based on the absolute pressure (which includes the reference pressure, which it turn takes into account the hydrostatic pressure induced by gravity) rather than the gauge pressure, how would I do so?
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Old   January 29, 2018, 18:15
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You would have to create your own field function, I think. I am not sure why one would want to do so, though. Can you elaborate on what you are trying to get out of it?

I would look at how the reference pressure is used before I go down the rabbit hole to make sure you are getting what you want out of it.

User Guide > Star-CCM+ > Post-Processing > Reporting Results > Specific Reports > Force Coefficient > Eq. 1154.
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drag, drag coefficient, reports, star ccm, vehicle. automotive

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