# Operating Pressure and Gauge pressure

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 September 30, 2019, 07:53 Operating Pressure and Gauge pressure #1 New Member   Yup Join Date: Sep 2019 Posts: 2 Rep Power: 0 Hi guys, I am trying to simulate nozzle flow conditions. I have a doubt regarding boundary conditions setup. If I want my far side domain outlet as pressure outlet set at atmospheric pressure. Then should I set my gauge pressure at 101325 while my operating pressure is set to 0? Or should I try with operating pressure set as 101325 and gauge pressure set to zero? Which one is correct and what is the difference between the two?

 September 30, 2019, 10:14 #2 Senior Member   Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,238 Rep Power: 63 In general, both will work. Having a non-zero operating pressure helps for machine precision (which isn't usually any issue nowadays). Some models specifically require a specific value for the operating pressure: some combustion models, some natural convection models, etc... Last edited by LuckyTran; September 30, 2019 at 12:54.

 September 30, 2019, 10:31 K-omega #3 New Member   Yup Join Date: Sep 2019 Posts: 2 Rep Power: 0 I am using K-omega with SST model. For this model, are there any specific requirements?

 September 30, 2019, 12:55 #4 Senior Member   Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,238 Rep Power: 63 Nothing special. Just use whatever combination is most aesthetically pleasing to you or helps you interpret the results more reasily.

 October 1, 2019, 08:04 #5 Senior Member     Paolo Lampitella Join Date: Mar 2009 Location: Italy Posts: 2,087 Blog Entries: 29 Rep Power: 38 It depends from case to case, but doesn't depend from the turbulence model. If most of your domain is around 101325 but you use 0 as reference, you are wasting 6 orders of magnitude in the pressure precision, i.e., you can see pressure differences only of order 1e-9/1e-10 instead of 1e-15/1e-16. If this matters or not depends from case to case. Of course, it is mandatory to get it right in single precision

 Tags ansys 19.2, boundary condition, pressure out