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asghari April 22, 2007 08:02

fixing pressure in some cells

How can we set gauge pressure in some cells to a desired value?

Is it neccessary to write a UDF for this purpose?


Tim Magurie April 26, 2007 12:59

Re: fixing pressure in some cells
Usually you would just set the pressure at a boundary condition. Can you define the geometry you are modeling so as to help define where you would need this pressure specified.

Asghari April 27, 2007 03:36

Re: fixing pressure in some cells
Ok, my geometry is a 2D Mixing Elbow and there are two inlet boundary in my geometry with difference inlet gauge pressures .I did'nt find in Manual how to adjust/set difference inlet gauge pressures. For example suppose :

Gauge pressure at inlet boundary 1 is:



Gauge pressure at inlet boundary 1 is:


How can I adjust this problem for instance using the Velocity-inlet boundary type.Also velocities in inlet are exactly specified and equal with 1m/s.

Thanks a lot .

Tim Magurie April 27, 2007 08:35

Re: fixing pressure in some cells
The way to do this is to not set your boundaries as velocity inlets, put as pressure inlets. Then you can specify the pressure at those two points. Just make sure your outlet boundary condition is also setup.

Asghari April 27, 2007 12:05

Re: fixing pressure in some cells
Thank you.

Yes, But there is a problem in my settings. I must set either pressure and velocity synchronously .

I read Manual for setting of pressure inlet boundary condition type . I felt it is well to bring to the notice of you , the section that describes this boundary condition as follows :

"Pressure inlet boundary conditions are used to define the fluid pressure at flow inlets,along with all other scalar properties of the flow. They are suitable for both incompressible and compressible flow calculations. Pressure inlet boundary conditions can be used when the inlet pressure is known but the flow rate and/or velocity is not known.This situation may arise in many practical situations, including buoyancy-driven flows.Pressure inlet boundary conditions can also be used to define a "free" boundary in an external or unconfined flow."

as you consider, for this boundary condition type, we can only set pressure at inlet and velocity evaluates in solution processes and it is impossible to set pressure & velocity syncronously, but inlet velocity is perfectly set to 1m/s in the my case and also I brought for you inlet pressure values in previous message. Therefore I can't use pressure inlet for this case. Can I use UDF for fixing of gauge pressure in inlet ?

Have you a better idea for this problem?

Thanks in advance for your kind attention.

imaduddin May 13, 2007 12:07

Re: fixing pressure in some cells
as far as i know, pressure inlet BC could define velocity inlet sychronously with pressure as a total pressure quantity. If we assuming the static pressure inlet equal to zero, then the total pressure will be equal with velocity pressure ==> (0.5*rho*v^2). I've been trying this and it's work, as long as we keep the pressure difference between pressure inlet and pressure outlet.


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