Pressure farfield vs Velocity Inlet BC

DarrenC · September 15, 2009, 10:54

Hi everyone,

First Post!! Hope you guys can help me out with my query.

I have a problem understanding the difference btw a pressure farfield and Velocity-inlet boundary conditions, and how they can be applied. Firstly let me describe my work.

Im setting up a transient simulation of a 3d wing transitioning from 0 - 15 degrees angle of attack. If I simulate this wing on air, I use ideal gas law and i can define a pressure farfield boundary condition. My farfield geometry is a huge sphere by the way and my wing geometry is in the middle of this sphere.

Now lets say I were to simulate this in a water medium, my farfield velocities will be much smaller and thus I will use a incompressible flow solution. But once I set density to constant, I will need to define a new type of BC for my farfield as pressure farfield does not work with incompressible flow. Now what type of BC should I set my farfield to? Velocity-Inlet?

Now I do not really understand how the velocity inlet BC works compared to pressure farfield. Mainly, will it even work with a spherical farfield boundary geometry, or do I have to split my sphere into 2 and define one as my inlet, and the other my outlet?

Also to give some more information about my simulation, I am using a UDF to change the velocity components of the flow at each time step to simulate the wing pitching up. Do you forsee any problems with this if velocity inlet is used?

I hope some of you can shed some light into this for me. Thanks in advance for your help.

makaero · September 16, 2009, 03:23

My work is similar to you, but the domain for 3d wing i used is a cubiod....trying to solve using Pre-farfield BC for subsonic flow.

May i knw the significance of using a sphere domain? how does it defer from cuboid domain (a wing face attached to a face of cuboid and the other end is free)

September 15, 2009, 10:54	Pressure farfield vs Velocity Inlet BC	#1
DarrenC Member Join Date: Sep 2009 Posts: 69 Rep Power: 17	Hi everyone, First Post!! Hope you guys can help me out with my query. I have a problem understanding the difference btw a pressure farfield and Velocity-inlet boundary conditions, and how they can be applied. Firstly let me describe my work. Im setting up a transient simulation of a 3d wing transitioning from 0 - 15 degrees angle of attack. If I simulate this wing on air, I use ideal gas law and i can define a pressure farfield boundary condition. My farfield geometry is a huge sphere by the way and my wing geometry is in the middle of this sphere. Now lets say I were to simulate this in a water medium, my farfield velocities will be much smaller and thus I will use a incompressible flow solution. But once I set density to constant, I will need to define a new type of BC for my farfield as pressure farfield does not work with incompressible flow. Now what type of BC should I set my farfield to? Velocity-Inlet? Now I do not really understand how the velocity inlet BC works compared to pressure farfield. Mainly, will it even work with a spherical farfield boundary geometry, or do I have to split my sphere into 2 and define one as my inlet, and the other my outlet? Also to give some more information about my simulation, I am using a UDF to change the velocity components of the flow at each time step to simulate the wing pitching up. Do you forsee any problems with this if velocity inlet is used? I hope some of you can shed some light into this for me. Thanks in advance for your help. jecs likes this.

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September 16, 2009, 03:23	hi	#2
makaero Member ANIL Join Date: Apr 2009 Posts: 35 Rep Power: 17	My work is similar to you, but the domain for 3d wing i used is a cubiod....trying to solve using Pre-farfield BC for subsonic flow. May i knw the significance of using a sphere domain? how does it defer from cuboid domain (a wing face attached to a face of cuboid and the other end is free)