why? whats the reason for setting both gauge total pressure and intial gauge pressure

sanjiiv · May 21, 2016, 01:34

hello,
In the,analyses of compressible flow over CD nozzle problem,
we will set the two variant pressure at the pressure inlet, one is gauge total pressure as 101325 pa and other is supersonic/initial gauge pressure as 99348 pa.why we are setting like this, what is the logic behind it...

LuckyTran · May 21, 2016, 12:14

I answered this in your other thread. Please don't make multiply threads all asking the same questions.

There are only two cases where the supersonic / initial gauge pressure value is used. The name of the box reflects these two uses.

1) When your inlet is supersonic, the flow properties at the inlet do not depend on the anything occurring downstream (in the domain). Hence when the inlet is supersonic, you must completely specify all properties at the inlet. For the supersonic case, you must specify both the stagnation and static pressure (both in gauge pressures, because everything in Fluent is gauge pressures). If your inlet is not supersonic, then the supersonic gauge pressure input is never needed and never used. You can put in any number and it will be ignored.

2) During the initialization, if you choose compute from and select the inlet, it will use the static pressure you have specified in the supersonic / initial gauge pressure. A lot of people choose to do their initialization this way, although I personally never do it.

You Fluent user's guide has all this information neatly written. In general, if you run into these types of problems and get confused, just click the help button.

May 21, 2016, 01:34	why? whats the reason for setting both gauge total pressure and intial gauge pressure	#1
sanjiiv New Member sanjeev kumar.m Join Date: May 2016 Posts: 13 Rep Power: 9	hello, In the,analyses of compressible flow over CD nozzle problem, we will set the two variant pressure at the pressure inlet, one is gauge total pressure as 101325 pa and other is supersonic/initial gauge pressure as 99348 pa.why we are setting like this, what is the logic behind it...

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May 21, 2016, 12:14		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,665 Rep Power: 65	I answered this in your other thread. Please don't make multiply threads all asking the same questions. There are only two cases where the supersonic / initial gauge pressure value is used. The name of the box reflects these two uses. 1) When your inlet is supersonic, the flow properties at the inlet do not depend on the anything occurring downstream (in the domain). Hence when the inlet is supersonic, you must completely specify all properties at the inlet. For the supersonic case, you must specify both the stagnation and static pressure (both in gauge pressures, because everything in Fluent is gauge pressures). If your inlet is not supersonic, then the supersonic gauge pressure input is never needed and never used. You can put in any number and it will be ignored. 2) During the initialization, if you choose compute from and select the inlet, it will use the static pressure you have specified in the supersonic / initial gauge pressure. A lot of people choose to do their initialization this way, although I personally never do it. You Fluent user's guide has all this information neatly written. In general, if you run into these types of problems and get confused, just click the help button.