# what is meant by Operating Pressure in Fluent?

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 March 9, 2013, 03:51 what is meant by Operating Pressure in Fluent? #1 New Member   Mifrah Ali Join Date: Mar 2013 Posts: 3 Rep Power: 13 hello all, i am a new user in Fluent. i want to know what exactly is meant by operating pressure in fluent? its default value is 101325 pa, is it atmospheric pressure? but sometime we also assume 0 as operating pressure, its making me feel dizzy.... what will be the operating pressure in 10 meter depth of a pool?

 March 9, 2013, 05:40 #2 Senior Member   Join Date: Aug 2011 Posts: 421 Blog Entries: 1 Rep Power: 21 It depends on how you model the density. It is always valid to set the operating pressure to (approximately) the mean pressure of the flow field. But it is only when you model the density using incompressible ideal gas law, or you are dealing with low-Mach-number compressible flow that the value of operating pressure is important. The operating pressure is not used if the density is modeled to be constant. You should check the Fluent user manual because it has more detailed and accurate description of the operating pressure.

 March 9, 2013, 12:38 #3 New Member   Mifrah Ali Join Date: Mar 2013 Posts: 3 Rep Power: 13 in my case density is constant so it means i can take operating pressure as zero??????

 March 9, 2013, 15:16 dear .... #4 Member   farzadpourfattah Join Date: Mar 2013 Posts: 41 Rep Power: 13 when you set pressure of operation condition 0 pascal, you prevent reverse flow in your domain.

 March 10, 2013, 01:15 #5 Senior Member   Join Date: Aug 2011 Posts: 421 Blog Entries: 1 Rep Power: 21 Yes. You can set operating pressure to any value because it is not used in case of constant density. chaitanyaarige likes this.

 March 12, 2013, 14:02 #6 New Member   Mifrah Ali Join Date: Mar 2013 Posts: 3 Rep Power: 13 Thank you

 June 8, 2013, 12:13 #7 Senior Member   FHydro Join Date: Jan 2013 Posts: 197 Rep Power: 13 what is that value in VOF model? (water+air)

 June 15, 2013, 11:27 vof #8 Member   farzadpourfattah Join Date: Mar 2013 Posts: 41 Rep Power: 13 if you set value of water 1 in a zone,value of air will be 0 at same zone.

June 6, 2016, 12:57
#9
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rizky djon hansemit
Join Date: Mar 2016
Posts: 2
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Quote:
 Originally Posted by blackmask It depends on how you model the density. It is always valid to set the operating pressure to (approximately) the mean pressure of the flow field. But it is only when you model the density using incompressible ideal gas law, or you are dealing with low-Mach-number compressible flow that the value of operating pressure is important. The operating pressure is not used if the density is modeled to be constant. You should check the Fluent user manual because it has more detailed and accurate description of the operating pressure.

can you tell us how do we know the mean pressure of the flow field in fluent. in my case i simulate 2d vawt in a wind tunnel. is there any consideration when we want to specify certain value of operating condition in fluent for incompressible ideal gas air. what about reference pressure location? its default value is [0,0,0]. how to specify the right reference pressure location in our simulation? please help us

 June 12, 2016, 17:49 #10 New Member   rizky djon hansemit Join Date: Mar 2016 Posts: 2 Rep Power: 0 is there any help?

September 20, 2017, 00:07
#11
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Parag Mangave
Join Date: Sep 2017
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Quote:
 Originally Posted by blackmask It depends on how you model the density. It is always valid to set the operating pressure to (approximately) the mean pressure of the flow field. But it is only when you model the density using incompressible ideal gas law, or you are dealing with low-Mach-number compressible flow that the value of operating pressure is important. The operating pressure is not used if the density is modeled to be constant. You should check the Fluent user manual because it has more detailed and accurate description of the operating pressure.
i am trying to simulate flow over blunt bodies my conditions are 100500pa, 303k,1.1551 density, what should be my operating pressure and guage pressure?

 September 20, 2017, 09:01 #12 Senior Member   Join Date: Nov 2013 Posts: 1,965 Rep Power: 26 You choose! Real pressure = operating pressure + guage pressure. If you want the real pressure to be 100500 Pa, you can set operating pressure at 100500 Pa, and then at the boundary set 0 Pa. Or set the operating pressure at 100000 Pa, and the pressure at the boundary at 500 Pa. Or the operating pressure at 0 Pa, and the pressure at the boundary at 100500 Pa. Physically, it is all the same. Exactly the same, identical. Only numerically, it is helpful to have smaller numbers for guage pressures, so put your operating pressure close to the 'average' pressure in your system. Extreme example: don't set your operating pressure at 10000100500 Pa, and your guage pressure at -10000000000 Pa, you will get numerical problems. tariq, chaitanyaarige, paragmangave and 2 others like this.

 September 20, 2017, 09:11 #13 New Member   Parag Mangave Join Date: Sep 2017 Posts: 6 Rep Power: 8 Also is prism layer generation necessary for supersonic speed?. Without using prism layer mesh can I use k omega or k epsilon turbulence model?

 October 26, 2017, 05:47 #14 New Member   Rouven Join Date: Oct 2017 Posts: 1 Rep Power: 0 A Question regarding this Operation Pressure: I have a low-Mach-No. Simulation and i know that the pressure inside my geometry should be s.th. about 7-8bar. So i set the operation Pressure to 7 bar. As result I got a pressure value of 1bar in the interior. So does this mean that I have to add 1 bar to the operation pressure to get the "real" value of pressure? Actually I have 1 bar beyond the inlets and outlets. Does this operation pressure influence my "outside"-conditions? So if I want 1 bar outside, do i have to set the pressure boundary condition to -6bar because 7bar minus 6 bar is 1bar? Best regards

 March 9, 2018, 06:11 #15 New Member   Hongyang Chen Join Date: Mar 2018 Location: Shanghai Posts: 1 Rep Power: 0 “ANSYS Fluent provides a “floating operating pressure” option to handle time-dependent compressible flows with a gradual increase in the absolute pressure in the domain. This option is desirable for slow subsonic flows with static pressure build-up, since it efficiently accounts for the slow changing of absolute pressure without using acoustic waves as the transport mechanism for the pressure build-up. Examples of typical applications include the following: 1.combustion or heating of a gas in a closed domain 2.pumping of a gas into a closed domain Limitations: The floating operating pressure option should not be used for transonic or incompressible flows. In addition, it cannot be used if your model includes any pressure inlet, pressure outlet, exhaust fan, inlet vent, intake fan, outlet vent, or pressure far field boundaries.“ From ANSYS FLUENT help document.

 May 11, 2018, 01:26 #16 New Member   BHOLU KUMAR Join Date: May 2018 Posts: 10 Rep Power: 8 Suppose I have set intet pressure = 405300 Pa (Fluent solver) Outlet gauge pressure = 4000 Pa Operating pressure = 0 Pa Then A/C you Real Pressure at inlet = 405300+0 = 405300 Pa outlet pressure gauge pressure = 4000 + 0 = 4000 Pa only ?

May 11, 2018, 05:31
#17
Senior Member

Kushal Puri
Join Date: Nov 2013
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Quote:
 Originally Posted by BHOLU Suppose I have set intet pressure = 405300 Pa (Fluent solver) Outlet gauge pressure = 4000 Pa Operating pressure = 0 Pa Then A/C you Real Pressure at inlet = 405300+0 = 405300 Pa outlet pressure gauge pressure = 4000 + 0 = 4000 Pa only ?
Yes if you are using 0 operating pressure the you have to apply absolute value of pressure at outlet also

 May 11, 2018, 06:16 #18 New Member   BHOLU KUMAR Join Date: May 2018 Posts: 10 Rep Power: 8 Thank you Kushal.

 May 16, 2018, 09:14 Operating pressure #19 New Member   Nitesh Kumar Join Date: May 2016 Posts: 17 Rep Power: 9 Hi Bholu, Did you get the desired result.

 December 4, 2018, 05:59 #20 New Member   Fab Join Date: Dec 2018 Posts: 13 Rep Power: 7 Hi all, Thanks for all your answer. What about if i want to calculate in a bend pipe the pressure losses and the poutlet is 10bar in a incompressible fluid? From what i understood: a) operating pressure= 10 bar b) gauge pressure = 0 bar? Correct? Why my pressure in CFD post is not considering the operating pressure? Thanks

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