# See effect of gravity

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 October 27, 2018, 15:41 See effect of gravity #1 Senior Member   Hamed Abdul Majeed Join Date: May 2012 Location: New Orleans, LA, US Posts: 147 Rep Power: 12 If we turn on gravity in Fluent it calculates for modified pressure and the "absolute pressure" does not show the effect of gravity. How to do that in Fluent! What I do now is to define a custom field variable P = absolute pressure + (density*gravity*mesh_y) I plot P and it gives me the require pressure drop inclusive of the gravity effects! Is there an easier way to do this in Fluent post-processor? Thank you.

 October 27, 2018, 21:29 #2 Senior Member   Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,062 Rep Power: 60 No not really. The easiest way is to use a custom field function like you've already done. Another way could be to set the operating density to zero at the start. But you'd have to re-run the case. hamed.majeed likes this.

October 28, 2018, 09:32
#3
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Hamed Abdul Majeed
Join Date: May 2012
Location: New Orleans, LA, US
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Quote:
 Originally Posted by LuckyTran No not really. The easiest way is to use a custom field function like you've already done. Another way could be to set the operating density to zero at the start. But you'd have to re-run the case.
A folliw up question:
Why didn't fluent define such a pressure variable...to avoid any extra effort. Because without it the pressures don't make practical sense!

October 29, 2018, 09:31
#4
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Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
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Rep Power: 60
Quote:
 Originally Posted by hamed.majeed A folliw up question: Why didn't fluent define such a pressure variable...to avoid any extra effort. Because without it the pressures don't make practical sense!
Well the static pressure field in Fluent is referencing the pressure used in the momentum equation used by the solver which properly should never contains the contribution from gravity forces. So, in my opinion it is great that the static pressure field does not contain the hydrostatic part. This part of Fluent I would not want changed, ever.

So why isn't there another variable that does contain the hydrostatic part? In this situation, you'd use the reference density approach which Fluent does provide. So yes it is developer laziness.

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