1st order slip, Fluent, Urgent

Karan · November 3, 2013, 20:55

Can anyone help me with how to implement first order slip condition to simulate rarefied gas flow (Kn = 0.3-0.7) in Ansys Fluent 13. If there is a tutorial available online? Could not find any.

Thanks

flotus1 · November 4, 2013, 08:59

Fluent has a boundary condition called "low-pressure boundary slip" that corresponds to a first order slip boundary condition for rarefied flows.
It is only available for laminar simulations.
Searching in the fluent manual for the name of this boundary condition will bring up all the information you need.

Nevertheless, a Knudsen number of 0.3...0.7 is way beyond the slip flow regime so the results will be poor.

Karan · November 4, 2013, 16:08

Hello Flotus,

Thanks for your reply. The low pressure condition does not ask for any accomodation factor or any other parameter (like the velocity gradient at the all). Does Fluent define all those values by itself ?

Also from what i know, it is valid for flow over flat plates only (or maybe some airfoils with low curvature). I want simulations for a wavy wall (sinusoidal wave function). Do i need to write UDF for this ?

Thanks

flotus1 · November 4, 2013, 17:28

Accomodation factors and the other settings for the boundary condition become available in the materials tab as soon as the boundary condition is activated.
You are right, the derivation of this boundary condition implies a flat wall (curvature radius >> mean free path).
If you want the "correct" boundary condition for curved walls, a UDF is the only way.
However, even the slip boundary condition for curved walls implies a Knudsen number in the slip flow regime.

zhangdongjie · January 8, 2021, 07:01

Quote:

Originally Posted by flotus1

Accomodation factors and the other settings for the boundary condition become available in the materials tab as soon as the boundary condition is activated.
You are right, the derivation of this boundary condition implies a flat wall (curvature radius >> mean free path).
If you want the "correct" boundary condition for curved walls, a UDF is the only way.
However, even the slip boundary condition for curved walls implies a Knudsen number in the slip flow regime.

Low pressure boundary slip only works in 3D. How can I open this button in 2D?

November 3, 2013, 20:55	1st order slip, Fluent, Urgent	#1
Karan New Member Karan Bansal Join Date: Sep 2013 Posts: 9 Rep Power: 12	Can anyone help me with how to implement first order slip condition to simulate rarefied gas flow (Kn = 0.3-0.7) in Ansys Fluent 13. If there is a tutorial available online? Could not find any. Thanks

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November 4, 2013, 08:59		#2
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,399 Rep Power: 46	Fluent has a boundary condition called "low-pressure boundary slip" that corresponds to a first order slip boundary condition for rarefied flows. It is only available for laminar simulations. Searching in the fluent manual for the name of this boundary condition will bring up all the information you need. Nevertheless, a Knudsen number of 0.3...0.7 is way beyond the slip flow regime so the results will be poor.

November 4, 2013, 16:08		#3
Karan New Member Karan Bansal Join Date: Sep 2013 Posts: 9 Rep Power: 12	Hello Flotus, Thanks for your reply. The low pressure condition does not ask for any accomodation factor or any other parameter (like the velocity gradient at the all). Does Fluent define all those values by itself ? Also from what i know, it is valid for flow over flat plates only (or maybe some airfoils with low curvature). I want simulations for a wavy wall (sinusoidal wave function). Do i need to write UDF for this ? Thanks

November 4, 2013, 17:28		#4
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,399 Rep Power: 46	Accomodation factors and the other settings for the boundary condition become available in the materials tab as soon as the boundary condition is activated. You are right, the derivation of this boundary condition implies a flat wall (curvature radius >> mean free path). If you want the "correct" boundary condition for curved walls, a UDF is the only way. However, even the slip boundary condition for curved walls implies a Knudsen number in the slip flow regime.