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-   -   hydrostatic pressure in bouyant flow (http://www.cfd-online.com/Forums/cfx/22630-hydrostatic-pressure-bouyant-flow.html)

Atit May 31, 2006 06:47

hydrostatic pressure in bouyant flow
 
In CFX manual, it says that for the flow with bouyancy effect if the reference pressure is not zero, then the hydrostatic portion is not included in the output pressure by CFX-POST. By numeric value check, however, I found that

enthalpy change = Cp*(T2-T1) = Cv*(T2-T1) + [(Pref+Ps+rho*g*h)/rho]1 - [(Pref+Ps+rho*g*h)/rho]2

where Ps is the pressure from CFX-POST.

while Cp*(T2-T1) is not equal to Cv*(T2-T1) + [(Pref+Ps)/rho]1 - [(Pref+Ps)/rho]2

I was wondering why hydrostatic pressure is not included in the output pressure, but it is included in the output enthalpy from CFX-POST. Can anyone explain this to me?

Joe May 31, 2006 07:03

Re: hydrostatic pressure in bouyant flow
 
Expert parameter:

Name pressure reference value Type Real Default Value 0 Description The relative pressure to set at the pressure reference node.

Atit May 31, 2006 07:37

Re: hydrostatic pressure in bouyant flow
 
I think now I know the reason. The enthalpy is calculated from the absolute pressure, and the hydrostatic portion is included in the absolute pressure. I have checked the numeric values in CFX-POST for this already.

Atit May 31, 2006 07:38

Re: hydrostatic pressure in bouyant flow
 
Thank you for your suggestion, but I am sorry I can't understand. Could you explain me in more details?


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