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James Date September 2, 2004 04:18

Transient Boundary Conditions
Hi guys,

A simple question:

Which is the best way to apply a transient boundary condition i.e. time varying inflow condition using data from a look up table, rather than a user defined function f(t) in the CCL language?

I've used the CCL language to apply transient boundary conditions that are easily described by a mathematical function dependant on time, however, I was wondering what approach is best for boundary condition which aren't easily described by mathematical functions.

In CFX-4.3 I used to use a user FORTRAN routine called USERBCS, is a similar approach taken in CFX-5.7?

Regards James

test September 2, 2004 06:29

Re: Transient Boundary Conditions
Hi, You need not create use user-subroutine.. you can use the 1D or cloud interpolation function where in you can import the file containing the data of points Time vs variable. (the data can be either tab/comma seperated. one set of data on one line in notepad/wordpad) remember unlike in CFX-4 you need not have the first line representing the number of data points.

Go to Create--> Library objects--> User Functions in the pre window (define a name to the funtion being created).

Suppose you create a function called as myfunction, which specifies temperature as a funtion of time. The argument of the function would be time while the result would be temprature. Give the units the argument and result enclosed in square brackets.

you can eiher enter the data one by one or right click in the data box and click on import and import the file.

In the boundary condition tab, you can refer to this function as


where t refers to time

James Date September 2, 2004 08:11

Re: Transient Boundary Conditions

Thanks ever so much for your help, it seems pretty simple to set up, we'll compared with what you used to have to do in CFX-4.3.

Thanks again.


Robin September 8, 2004 16:52

Re: Transient Boundary Conditions
Hi James,

You could also create your own user defined CEL function, written in Fortran.

Regards, Robin

sharath September 13, 2004 03:20

Re: Transient Boundary Conditions
Hello, I want to know how I can incorporate transient boundary condition in Fluent.I have time dependant inlet velocity. Consider this as urgent. Thanks in advance. sharath.

Robin September 13, 2004 11:34

Re: Transient Boundary Conditions
Try the Fluent forum.

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