# Pressure BC for combustion chamber

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 August 19, 2009, 12:29 Pressure BC for combustion chamber #1 New Member   Giuki Cael Join Date: May 2009 Location: Belgium/The Netherlands Posts: 13 Rep Power: 16 Dear all, I have some trouble understanding all the parameters for setting up pressure boundary conditions in Fluent. I have a combustion chamber with annulus to simulate. At this stage cold flow is considered. I'm using velocity inlet or mass flow inlet at the moment under standard operating conditions. I would like to simulate the chamber under the right pressure. Which would mean the flow entering the annulus at my inlet BC should be under a pressure of approx. 41.6 bar. I want to achieve a pressure drop between 4-5% over my chamber. Let's say for now a pressure drop of 2 bar. So now in Fluent I can change: Operating pressure Pressure inlet: Gauge pressure Initial/supersonic gauge pressure Pressure outlet: Gauge pressure I know that the total pressure is equal to the gauge pressure added with operating pressure. And that by initial/supersonic pressure the static pressure is meant. But that doesn't help me much in setting the right values. I've tried setting operating pressure at 39.6 bar and setting the Gauge pressure at my inlet at 2 bar and 0 gauge at my exit BC. I have doubts whether this represents the physical situation. Does anybody has an idea how I should set them right and why? Thank you!

 July 19, 2011, 11:35 #2 New Member   Join Date: Aug 2009 Posts: 5 Rep Power: 16 Hi Giuki, I am stuck with the same kind of problem... My settings for the combustion chamber (simple cylinder) : Air inlet BC: mass flow inlet gas inlet BC: mass flow inlet outlet: pressure outlet, gauge pressure = 0. the operating pressure was set to 5 bar (its the air inlet pressure) steady state, species transport, cold flow ... with the above settings fluent gives out following results for Absolute pressure: outlet: 5bar Air inlet: 4,6 bar Gas inlet: 4,7 bar... as u can see the outlet pressure is higher than the inlet pressure.. Could u help me ...