## Fluids

Topics relate to Fluent, CFX, Turbogrid and more

#### Ansys fluent does not considerd the pressure boundary condition

• Abhi9_Chavare
Subscriber

I am new to the ansys fluent,

I have applied the pressure as boundary condition in a pipe caring the compressible fluid, at inlet 500000pa and outlet 100000pa but the ansys fluent do not coverge to the inlet boundary pressure condition

• Nikhil Narale
Ansys Employee
Hello,

In my opinion, for pressure inlet and pressure outlet boundary conditions, the solution is quite sensitive to the initial guess (Initial gauge pressure). Also, please be informed that it is total gauge pressure at the intel and static pressure at the outlet, while defining boundary conditions.
One of the images you shared looks like an attachment, which we are not allowed to download. Can you please post the image directly in the comment section and not attach it?
1: 43.7.17. Pressure Inlet Dialog Box (ansys.com)
2: 7.4.3. Pressure Inlet Boundary Conditions (ansys.com)

If you are not able to access above links, please refer to this forum discussion: Using Help with links ÔÇö Ansys Learning Forum

Nikhil
• Abhi9_Chavare
Subscriber
Thanks The attachment was same as image I cann't open the links Please paste the data here.

• Rob
Forum Moderator
• Abhi9_Chavare
Subscriber
Thanks, Rob.
Now I can access the link, Thanks.
I have gone through it
But I don't understand why the inlet and outlet boundary conditions are not satisfied.
As Ansys Fluent does not reach the provided boundary conditions
As mentioned :
TheSupersonic/Initial Gauge Pressureis ignored by Ansys Fluentwhenever the flow is subsonic, in which case it is calculated from the specified stagnation quantities. If you choose to initialize the solution based on the pressure-inlet conditions, theSupersonic/Initial Gauge Pressurewill be used in conjunction with the specified stagnation pressure to compute initial values according to the isentropic relations (for compressible flow) or BernoulliÔÇÖs equation (for incompressible flow). Therefore, for a sub-sonic inlet it should generally be set based on a reasonable estimate of the inlet Mach number (for compressible flow) or inlet velocity (for incompressible flow).
but i have applied the outlet condition as initial gauge pressure to initalize.
• DrAmine
Ansys Employee
You are looking into static pressure field. Check the total pressure field.
• Abhi9_Chavare
Subscriber
Thanks, I got it but can you please through the light on it as the velocity increase (doubled).
• DrAmine
Ansys Employee
How shall I do that?
• Abhi9_Chavare
Subscriber
-You are looking into static pressure field. Check the total pressure field.
Please light on the static and total pressure when to use, and its importance.

• Abhi9_Chavare
Subscriber
i.e When I applied the inlet and outlet condition only Pressure so there will be the static pressure
As total pressure =static pressure + dynamic pressure (due to velocity)
When velocity is zero the Pressure must be equal to static
At the inlet the velocity is zero but in static pressure the fluent does not converge to the boundary conditions.