# Table or polynomial boundary condition

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March 15, 2019, 11:33
Table or polynomial boundary condition
#1
New Member

Luka Vincekovic
Join Date: Mar 2019
Posts: 6
Rep Power: 2
Hi all,
I am trying to insert flow direction as boundary condition via table. As far as I realised this can't be done. It is either value or expression, right?

So my question is, if I have a table which for example, describes some boundary condition what is the best way to import it as an expression?
Can someone please explain the procedure?

Let's say that we start from 100x100 values x-y table which describes total pressure. How do you get polynomial and import it in CFX? I attached how the pressure looks like when you plot it in MATLAB.

Thanks, Luka

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 March 15, 2019, 11:38 #2 Senior Member   Join Date: Jun 2009 Posts: 962 Rep Power: 17 In ANSYS CFX, a table is an expression via a function. Check the documentation for how functions work in expressions.

 March 15, 2019, 11:41 #3 New Member   Luka Vincekovic Join Date: Mar 2019 Posts: 6 Rep Power: 2 Yeah, I managed to get an expression working but it doesn't show what I want. Do you have an idea how to describe attached contour with polynomial that would work? Thanks

 March 15, 2019, 18:03 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 15,628 Rep Power: 120 You could use a 3D interpolation function, a polynomial which describes the function as a CEL expression or a user fortran routine to define it. CFX has lots of ways to do it. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

 March 18, 2019, 11:34 #5 Senior Member   Erik Join Date: Feb 2011 Location: Earth (Land portion) Posts: 837 Rep Power: 16 Yes, there are lots of ways to do it. Easiest would be the 3D interpolation function that uses your 100x100 table directly. Make it a function of (x,1,z) format your table with 4 columns, using: x, 1, z, PressureValue. Then make an expression for P_inlet which would be a call to the function: PressureFunction(x,1,z). To make a polynomial, you will have to develop an equation for a 2D surface, which is difficult, and usually not very accurate for complex surfaces.

 March 19, 2019, 04:30 #6 New Member   Luka Vincekovic Join Date: Mar 2019 Posts: 6 Rep Power: 2 Thank you all for the help, just a quick update. I managed to import all the data as a table at the end. It is possible to import also the velocity direction as a table. I did a bit of reverse engineering. So in CFX Post you can see what data you can export from your boundaries and all these data can be imported as a table into CFX Pre. So I took a table from CFX Post and just changed the values with what I needed and put it into CFX Pre.

 March 20, 2019, 12:15 #7 Senior Member   Erik Join Date: Feb 2011 Location: Earth (Land portion) Posts: 837 Rep Power: 16 Yes you can import velocity as a table, or just about anything else you wish.

 Tags cfx, polynomial bc, polynomial eqn.