# Help: operating pressure for deflagration

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 October 18, 2010, 10:42 Help: operating pressure for deflagration #1 New Member   Join Date: Mar 2009 Posts: 19 Rep Power: 10 Hello, everybody, I am doing simulation of deflagration in a tunnel (flame propagation of premixed mixture). The mixture is ignited at one closed end of the tunnel. First, the Mach number <0.1, however,the flow velocity increase fast with time, and the Mach number also increase to a number larger then 0.1. The reaction flow is treated as compressible flow. The problem is how should I set the operating pressure in FLUENT6.3.26? It's suggested in Fluent that when Mach number <0.1, operating pressure=mean flow pressure, while when Mach number >0.1, operating pressure=0 or mean flow pressure. So what can I do.？ By the way, I use the density-based solver, so I can not use the floating operating pressure. Thanks very much! Last edited by fireman; October 18, 2010 at 11:54.

 October 19, 2010, 10:07 #2 New Member   sreenivasa rao gubba Join Date: Sep 2010 Location: Leeds University, UK Posts: 27 Rep Power: 9 Hi check if you can overide by writing an udf in fluent? It is my guess only. Sree

 October 19, 2010, 10:14 #3 New Member   Join Date: Mar 2009 Posts: 19 Rep Power: 10 hi, Sree Thank you. but I can not find the udf choice of operating pressure.

 October 19, 2010, 11:01 #4 New Member   sreenivasa rao gubba Join Date: Sep 2010 Location: Leeds University, UK Posts: 27 Rep Power: 9 hi Fireman Can you clearly define, what do you mean by operating pressure. Do you want to set the entire domain at a pressrure equal to the experimental pressure? Do you want to devide your domain and setup two different pressure? Just eloborate a bit please. Sree

 October 19, 2010, 11:43 #5 New Member   Join Date: Mar 2009 Posts: 19 Rep Power: 10 hi Sree, The operating pressure in fluent is used to reduce the roundoff error for low-Mach flow. I want to setup the operating pressure equal to the mean flow pressure of the whole domain. Or I need setup the operating pressure=mean flow pressure when Mach No.<0.1, operating pressure=0 when Mach No.>0.1 Now I don't know how to realize either of the two settings described above. Thank you very much

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