CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > FLUENT

Gauge pressure in 'Pressure outlet' boundary conditions, if operating pressure given

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   April 12, 2016, 12:24
Default Gauge pressure in 'Pressure outlet' boundary conditions, if operating pressure given
  #1
New Member
 
Anil Prajapati
Join Date: Mar 2015
Posts: 2
Rep Power: 0
anilprajapati607 is on a distinguished road
I am simulating gas turbine blade (3d) with in compressible air & subsonic flow. I used 'velocity inlet' at inlet since I know the velocity. The operating pressure is 15 bar. I am using ' pressure outlet ' at outlet boundary which asks me about the gauge pressure. I am confused whether this value is 15 bar or not? How much this effects in the process?

Hoping for your reply.
Anil

Last edited by anilprajapati607; April 13, 2016 at 23:22.
anilprajapati607 is offline   Reply With Quote

Old   April 12, 2016, 17:04
Default
  #2
Senior Member
 
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,750
Rep Power: 66
LuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura about
You need to specify the gauge pressure at the outlet relative to the set operating pressure.

The default operating pressure in Fluent is 101325 Pa. Did you modify this to reflect the 15 bar?

Whatever the operating pressure is in Fluent (if you used the default or change it), subtract this operating pressure from the absolute static pressure at the outlet and use that as the gauge pressure for your outlet.
LuckyTran is offline   Reply With Quote

Old   April 13, 2016, 13:26
Default
  #3
New Member
 
Anil Prajapati
Join Date: Mar 2015
Posts: 2
Rep Power: 0
anilprajapati607 is on a distinguished road
Quote:
Originally Posted by LuckyTran View Post
You need to specify the gauge pressure at the outlet relative to the set operating pressure.

The default operating pressure in Fluent is 101325 Pa. Did you modify this to reflect the 15 bar?

Whatever the operating pressure is in Fluent (if you used the default or change it), subtract this operating pressure from the absolute static pressure at the outlet and use that as the gauge pressure for your outlet.
Thank you LuckyTran for your reply.

For my simulation I have values for inlet velocity and operating pressure. At outlet if I use 'pressure outlet' boundary condition and use any static pressure value, I will get the same value at outlet after simulation.
The thing is I am trying to check the differences in pressure at inlet and outlet. Does it make any sense if I use 'pressure outlet' boundary condition at outlet ( I mean I will get the constant given value always)? Should I use any other outlet boundary condition instead of 'pressure outlet' in my case so that I can calculate the differences in pressures?

Hoping for your reply.
anilprajapati607 is offline   Reply With Quote

Old   April 13, 2016, 14:17
Default
  #4
Senior Member
 
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,750
Rep Power: 66
LuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura about
I think you are using "operating pressure" in the casual sense and not the Fluent sense. You define a reference pressure in Fluent. This reference pressure is called "operating pressure." But let's call it reference pressure. Regardless, this reference pressure can be anything. Now all that remains is either an inlet pressure or an outlet pressure.

You want to specify velocity at the inlet (and not pressure). Then you want to specify pressure at the outlet. These are boundary conditions and are therefore fixed. Whatever your simulation does, it cannot change from these fixed values. So yes, your outlet pressure will be whatever it is specified to be (because it was specified). There shouldn't be any confusion here. You are specifying the outlet pressure, therefore the outlet pressure must be fixed. If you want to specify the outlet pressure as 15 bar, then do so. If not, then what is your outlet pressure?

As long as you do not specify the inlet static pressure (which you can't anyway), then you will always be able to calculate the static pressure drop. The best you can do is specify the inlet stagnation pressure.
LuckyTran is offline   Reply With Quote

Reply

Tags
gauge pressure, operating pressure, pressure outlet, subsonic flow

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
sliding mesh problem in CFX Saima CFX 46 September 11, 2021 08:38
Setting both inlet and outlet with pressure boundary conditions ahmadbakri CFX 0 July 1, 2015 05:06
Radiation interface hinca CFX 15 January 26, 2014 18:11
Error finding variable "THERMX" sunilpatil CFX 8 April 26, 2013 08:00
RPM in Wind Turbine Pankaj CFX 9 November 23, 2009 05:05


All times are GMT -4. The time now is 09:09.