Learning Forum

[manelaero2020]

Hi everybody ; 
I have two questions about pressure BC in Ansys fluent :
1/ Is total gauge pressure = Gauge pressure + Operating pressure ? (with total gauge pressure is the isentropic pressure and gauge pressure is the static pressure in the fluid ? )
2/ Do you think that in case of compressible interior flow ( in a nozzle for example); it is recommended to set operating pressure to 0? On the other side, do you think that in case of compressible exterior flow ( supersonic flow over a wing for example ); it is recommended to set operating pressure to P atm?
3/ At your point of view, in which case we can set pressure inlet BC and in which case we can set FAR FIELD PRESSURE BC? ( i talk about compressible flow in both cases) 
I am very thankful for your help 
Kind regards 

[Karthik Remella]

nTotal gauge pressure is still gauge pressure. It is simple the fluid pressure in isentropic conditions. Gauge pressure + Operating pressure = Absolute pressure. nIn most cases, you will be using the ideal gas law to model compressible flow. You should be able to set the operating pressure to 0. But, make sure that you appropriately adjust your total gauge pressure conditions to reflect the same absolute pressure. This is the most important step.nIf you are working on an external flow simulation, it is recommended that you use the 'Far Field Pressure BC'. This is a better physical representation of free-stream condition at infinity. However, there are some limitations:nIdeal-gas law must be chosen.nIncompatible with multiphase modelsnCannot apply this BC with constant density flows.nI hope this addresses your question. nThank you.nBest,nKarthikn

[manelaero2020]

Hello @Kremella  ;nFirstly thank you for the reply.nIn incompressible flows course , we have shown that total pressure = static pressure +dynamic pressure.nIn compressible flow course , please check file below. The hypothesis is isentropic flow ( ideal gas) nSO , to solve our problem ( i am trying to solve compressible flow in a nozzle , so trying to understand pressure BC in Fluent) , we must know Total pressure and static pressure at the inlet and the outlet. nMy problem remains : nWhat is total pressure and static pressure for Ansys Fluent ? ( like i have written in the file below) ? nAs you know Fluent proposes : n1/ Gauge pressuren2/ Total Gauge pressure n3/ Absolute pressure = Gauge pressure+operating pressure n4/ Supersonic initial gauge pressure n( there is no problem for oprerating pressure : it is a floating pressure , not considered by fluent )If you can answer me also this question please :nFluent proposes an option : Back flow pressure specification : a/ Total presssure b/ static pressure nWhat is the meaning please and what is the influence on results ? ( i have checked Fluent help , but still not clear )nnI hope i was clear and sorry for english mistakes.nKind regards n