Gauge Pressure vs Operating pressure

  • Last Post 4 days ago
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cehangir posted this 02 August 2018


I am working on combustion at high pressure. the model I want has operating pressure of 6 atm. 

For the boundary conditions for inlet and outlet in ANSYS FLUENT, pressure is shown as supersonic/gauge pressure. Should I be inputting 6 atm or should i input 5 atm (since Pgauge = Pabs - Patm) 

It is a simple question so I hope someone can clarify it to me 




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abenhadj posted this 02 August 2018

The supersonic/gauge pressure will be used by Fluent if the flow on entry is supersonic (3D case you need to give 5 boundary information as 0 information is provided from the domain) or if you want to initialize from it. You need to input the total pressure on your inflow boundary. Please check the Fluent User'S Guide when it talks about the Pressure Inlet Boundary Condition.

Every single pressure input in Fluent is a relative / gauge pressure input: relative to the operating pressure you provide. So If you have Total pressure = 6 atm Operating pressure is 5 atm then I will set the Total pressure at pressure inlet to 1 atm.


Best regards,


EngineerMech posted this 18 April 2019



I have related question please, what if I have inlet pressure=75bar  for fluid1(co2) and inlet pressure=4bar  for fluid2(water-ethylene glycol) in a contour flow heat exchanger, so please what is the best boundary condition set for inlet and outlet  



BSabrina posted this 6 days ago

Hi Sir,



Did you find the answer about your question!! I have a same question, please!!
Kind regards

abenhadj posted this 4 days ago

Pressure Inlet for both. Operating Condition pressure is only a shift pressure. It just helps to reduce round-off. Quite relevant if incompressible EOS is used or very low Mach number compressible flows.

Best regards,