Table or polynomial boundary condition

lvincek · March 15, 2019, 12:33

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

Opaque · March 15, 2019, 12:38

In ANSYS CFX, a table is an expression via a function. Check the documentation for how functions work in expressions.

lvincek · March 15, 2019, 12:41

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

ghorrocks · March 15, 2019, 19:03

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.

evcelica · March 18, 2019, 12:34

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.

lvincek · March 19, 2019, 05:30

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.

evcelica · March 20, 2019, 13:15

Yes you can import velocity as a table, or just about anything else you wish.

March 15, 2019, 19:03		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	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.

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March 15, 2019, 12:38		#2
Opaque Senior Member Join Date: Jun 2009 Posts: 1,880 Rep Power: 33	In ANSYS CFX, a table is an expression via a function. Check the documentation for how functions work in expressions.

March 15, 2019, 12:41		#3
lvincek New Member Luka Vincekovic Join Date: Mar 2019 Posts: 6 Rep Power: 7	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 18, 2019, 12:34		#5
evcelica Senior Member Erik Join Date: Feb 2011 Location: Earth (Land portion) Posts: 1,188 Rep Power: 23	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, 05:30		#6
lvincek New Member Luka Vincekovic Join Date: Mar 2019 Posts: 6 Rep Power: 7	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, 13:15		#7
evcelica Senior Member Erik Join Date: Feb 2011 Location: Earth (Land portion) Posts: 1,188 Rep Power: 23	Yes you can import velocity as a table, or just about anything else you wish.