# having trouble implementing airfoil with Wall Slip condition

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 December 21, 2014, 07:44 having trouble implementing airfoil with Wall Slip condition #1 New Member   Mohammad Hossein Khozaei Join Date: Nov 2011 Posts: 8 Rep Power: 13 Hello every body I need to solve my problem on airfoil with wall Slip condition. as i found, i can put this condition in 2 ways: 1. enter a wall velocity 2. enter specified shear on the wall In both the ways i need to enter velocity or specified shear with 2 components (x & y). The problem is, as the normal-vector of the wall is changing around the airfoil and the wall-velocity (and specified shear) are both tangential to the wall, I need to have a local-coordinate-system in each point of the airfoil-wall to enter the velocity due to the local-coordinate-systems. (or something like this) (I don't have the Airfoil-wall-equation) (I have to check the results in different slip lengths, 10% slip to 50%, not 100% or free slip) (and then it must be solved in a complicated 3-D geometry, so i can't split the wall into some semi-linear parts.) I don't know how to do this and whether it works or not. can any body help me ? please. I really appreciate it. PS. In easy words, 10% slip means velocity on the wall is 10% of free-stream (tangential to the wall) (wall-slip-condition can be defined by 3 (related) parameters: 1. specified shear 2. wall-velocity 3. slip length, the definitions are available in literature, but in CFX and Fluent i just can enter specified shear or wall velocity, you can find them in wall-boundary-detail under cover of mass and momentum) (to avoid mathematical equation it's better to define a wall velocity than specified shear) Last edited by Khozaei4000; December 22, 2014 at 02:00. Reason: Make it more complete.

 December 21, 2014, 17:07 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,323 Rep Power: 138 Or: 3. Go to the Boundary details tab and select Mass and momentum option: "Free slip wall". I think I would choose option 3.

December 22, 2014, 00:59
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 Originally Posted by ghorrocks Or: 3. Go to the Boundary details tab and select Mass and momentum option: "Free slip wall". I think I would choose option 3.
It's not a free-slip problem.
i have to check the results in different slip lengths (10% slip to 50%, not 100% or free slip)

 December 22, 2014, 01:32 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,323 Rep Power: 138 So why didn't you say that you want 10%-50% slip in the first post? Can you define mathematically want you want to do? In other words, if you want 10% slip, what actually is 10% slip defined as? And why do you want to use this model?

December 22, 2014, 01:49
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 Originally Posted by ghorrocks So why didn't you say that you want 10%-50% slip in the first post? Can you define mathematically want you want to do? In other words, if you want 10% slip, what actually is 10% slip defined as? And why do you want to use this model?
in easy words, 10% slip means velocity on the wall is 10% of free-stream (tangential to the wall) (wall-slip-condition can be defined by 3 (related) parameters: 1. specified shear 2. wall-velocity 3. slip length, the definitions are available in literature, but in CFX and Fluent i just can enter specified shear or wall velocity, you can find them in wall-boundary-detail under cover of mass and momentum) (to avoid mathematical equation it's better to define a wall velocity than specified shear)

I have to find influence of different percentage of wall-slip on Drag 'n Lift forces, velocity 'n pressure fields, etc. and the influence on some other parameters in complicated 3D model. that's it.

 December 22, 2014, 05:59 #6 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,323 Rep Power: 138 You probably know the free stream velocity as you defined your inlet and outlet boundary conditions to have a defined free stream condition. Therefore you know the velocity to apply at the wall. You can make sure it is tangential to the wall using the normal_x, normal_y and normal_z variables.

December 22, 2014, 06:46
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 Originally Posted by ghorrocks You probably know the free stream velocity as you defined your inlet and outlet boundary conditions to have a defined free stream condition. Therefore you know the velocity to apply at the wall. You can make sure it is tangential to the wall using the normal_x, normal_y and normal_z variables.
Thank you dear,
how can i obtain normal_x, normal_y and normal_y variables?
is there a CEL? can i write an expression for them ?

 December 22, 2014, 06:54 #8 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,323 Rep Power: 138 That should be the variable names. It should work in CEL expressions. It exists on wall boundary patches.

December 22, 2014, 07:12
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 Originally Posted by ghorrocks That should be the variable names. It should work in CEL expressions. It exists on wall boundary patches.
there is no such variables in CFX-Pre.

 December 22, 2014, 07:15 #10 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,323 Rep Power: 138 CFX-Pre does not have all variables in it. The solver has all the variables. So stick them in CFX-Pre, ignore the warning/error about variable names and see if the solver accepts them.

December 22, 2014, 07:21
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 Originally Posted by ghorrocks CFX-Pre does not have all variables in it. The solver has all the variables. So stick them in CFX-Pre, ignore the warning/error about variable names and see if the solver accepts them.
I'll give a try.

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