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Operating Pressure and Gauge pressure

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Old   September 30, 2019, 07:53
Default Operating Pressure and Gauge pressure
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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?
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Old   September 30, 2019, 10:14
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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...

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Old   September 30, 2019, 10:31
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I am using K-omega with SST model. For this model, are there any specific requirements?
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Old   September 30, 2019, 12:55
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Nothing special. Just use whatever combination is most aesthetically pleasing to you or helps you interpret the results more reasily.
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Old   October 1, 2019, 08:04
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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
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