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-   -   setup outlet boundary condition from steady state result (http://www.cfd-online.com/Forums/cfx/120930-setup-outlet-boundary-condition-steady-state-result.html)

shaswat July 17, 2013 11:20

setup outlet boundary condition from steady state result
 
Dear all

In my steady state analysis inlet is pressure (specified value) and outlet is velocity ( known value). later I want to run transient analysis. In this case, I would like to use the outlet as a pressure which is derived from the result of steady state at the outlet . please help me How to setup this condition?


Thank you

ghorrocks July 17, 2013 18:42

This is simple - just define the outlet as a pressure boundary and give it the pressure value from your steady state analysis. When you run the transient simulation use the steady state run as an initial condition.

kmgraju July 23, 2013 03:53

Quote:

Originally Posted by ghorrocks (Post 440416)
This is simple - just define the outlet as a pressure boundary and give it the pressure value from your steady state analysis. When you run the transient simulation use the steady state run as an initial condition.

In my transient analysis, I set initial velocity and relative pressure with suitable value. I didn't run the steady state simulation.

I set inlet with velocity as a function of time and I set the outlet boundary condition as areaAve(Pressure)@outlet.

I need to clarify the following basic questions.

1. Is it correct setting ?( I dont' know the pressure value at the outlet. note that I set initial velocity and pressure when t=0)
2. In my setting, is the areaAve(Pressure)@outlet means free pressure boundary condition?

Thank you

ghorrocks July 23, 2013 06:04

Do not specify the outlet as areaAve(Pressure)@Outlet! That is not going to work. You need to set it to a pressure value, probably just 0Pa.

What is a free pressure boundary condition? You have to set either the pressure or the velocity, and the other one is solved by the software.

kmgraju July 23, 2013 09:01

Quote:

Originally Posted by ghorrocks (Post 440416)
This is simple - just define the outlet as a pressure boundary and give it the pressure value from your steady state analysis. When you run the transient simulation use the steady state run as an initial condition.

areaAve( pressure)@outlet works in my case. How?

just define the outlet as a pressure boundary and give it the pressure value from your steady state analysis

can you please give one example I could not understand. How I can give the pressure value when the solution finishes steady state and start transient automatically?

( I may setup steady state and transient through configuration control )

Thank you

ghorrocks July 23, 2013 16:49

This is in effect setting the outlet pressure to the average it was last iteration. I have no idea what this is going to do, but I suspect you will have problems converging.

Have a look at the tutorial examples of how outlet boundaries are meant to be defined.


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