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-   -   having trouble implementing airfoil with Wall Slip condition (https://www.cfd-online.com/Forums/cfx/146210-having-trouble-implementing-airfoil-wall-slip-condition.html)

Khozaei4000 December 21, 2014 07:44

having trouble implementing airfoil with Wall Slip condition
 
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)

ghorrocks December 21, 2014 17:07

Or:
3. Go to the Boundary details tab and select Mass and momentum option: "Free slip wall".

I think I would choose option 3.

Khozaei4000 December 22, 2014 00:59

Quote:

Originally Posted by ghorrocks (Post 524872)
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)

ghorrocks December 22, 2014 01:32

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?

Khozaei4000 December 22, 2014 01:49

Quote:

Originally Posted by ghorrocks (Post 524890)
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.

ghorrocks December 22, 2014 05:59

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.

Khozaei4000 December 22, 2014 06:46

Quote:

Originally Posted by ghorrocks (Post 524910)
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 ?

ghorrocks December 22, 2014 06:54

That should be the variable names. It should work in CEL expressions. It exists on wall boundary patches.

Khozaei4000 December 22, 2014 07:12

Quote:

Originally Posted by ghorrocks (Post 524917)
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.

ghorrocks December 22, 2014 07:15

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.

Khozaei4000 December 22, 2014 07:21

Quote:

Originally Posted by ghorrocks (Post 524922)
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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