Kalyan Goparaju
Ansys Employee

Hello, 

Since Fluent deals with gauge pressures, these two problems, though prescribed differently, will even out to the same thing. In the steady state case, the operating pressure is being set to 100mm of Hg and since gauge pressure is being set to 0 (which means we are telling Fluent that gauge pressure is same as operating pressure), the absolute pressure is the sum of both i.e. 100mm of Hg (13332 Pa) or 100mm above the mean. In the transient case, the operating pressure is set to 1atm and gauge set to 13332 Pa, so the absolute pressure is 101325+13332 Pa or 100mm above the mean. So, the only difference between the two is that the reference baseline pressure is higher for the transient case, but from the standpoint of gauge pressures (which is what Fluent works with), it will be the same. Hope this helps. 

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