creating a field function
 

Hello,

I am working on a project where I have to simulate the flow of air through a pipeline.

I want to create the velocity inlet profile on star ccm+.

How do I implement this function into the program.

funktion :
-2E-08z^4 + 2E-05z^3 - 0,007z^2 + 1,03z- 4,578


Thanks in advance.
Can

(-2*pow(10,8)*(pow($$Centroid[2],4))) + (2*pow(10,5)*(pow($$Centroid[2],3))) - (0.007*(pow($$Centroid[2],2))) + (1.03*($$Centroid[2])) - 4.578

In the above formulation you can also use $$Position[2] instead of $$Centroid[2] is thats what you need.

To implement the field function on the boundary
Region > Boundaries> Physics Values > Velocity Magnitude (Method > field function)

(-2 * Pow (10.8) * (pow ($ $ Centroid [2], 4))) + (2 * pow (10.5) * (pow ($ $ Centroid [2], 3))) - (0.007 * (pow ($ $ Centroid [2], 2))) + (1.03 * (pow ($ $ Centroid [2], 1))) - 4.578

I have the equation changed(red color), ist dies correct?
and if I have this equation enter into the program, I get error message "Compiled field function type is not vector "

Thanks in advance.
Can

Try this, just copy and paste...

(-2 * pow (10,8) * (pow ($$ Centroid [2], 4))) + (2 * pow (10,5) * (pow ($$ Centroid [2], 3))) - (0.007 * (pow ($$ Centroid [2], 2))) + (1.03 * ($$ Centroid [2])) - 4.578

In the pow command variables are separated with commas. Also, no space between the two $$ signs.

Thank you for your effort, unfortunately, does not again.diese equation is a velocity distribution in a Pipe.
I have descriped cylindrical coordinatesystem in the Inlet .it must be the Origin in the middle? Part(Pipe) has a symmetry Plane :)

Sure that he need to write the E8 as a pow?
Normally it works without this fine?!

Hi,

I have changed the equation again.

-0.00000002 * (pow ($$ Centroid [2], 4)) + 0.00002 * (pow ($$ Centroid [2], 3)) -
0.007 *(pow($$ Centroid [2], 2)) + 1.03 * ($$ Centroid [2]) - 4.578

Unfortunately, I get the same error message again,"Compiled field function type is not vector "

Thanks

Have you changed the field function 'Type' to vector?

I don't get this error message. I am using an older version of STAR CCM+. I will check it with the new version later and let you know.

Hmm is the function set a scalar?

No, I have field function 'Type' Scalar. I am using version 4.2 of STAR CCM+. how did they coordinate system defined?

for vector definition, the three velocity components are described [x,y,z]. I guess in your case it would be

[0,0,-0.00000002 * (pow ($$ Centroid [2], 4)) + 0.00002 * (pow ($$ Centroid [2], 3)) -
0.007 *(pow($$ Centroid [2], 2)) + 1.03 * ($$ Centroid [2]) - 4.578]

4.2? You mean 4.02? ;)
In the properties you have the function type.
Make a screenshot.

You're right, it works fine. I like to use pow so that I dont miss a zero...

That is really unbelievable. This works. I am very grateful for their help:D

course V4.02:(

@SKK: Maybe you should make a benchmark for this extra pow function :D :D :D

A other way would be to use $Centroid_i (maybe a "cleaner" way).
Of cource you need the vector "style" for the velocity :D I make too much 2D :D

I want to do what OP did but with a parabolic velocity profile inlet. The eqaution would be
v(r) = Vm(1-(r^2/R^2)). What code would i have to implement.
thanks

You would have to implement reading User Guide p. 465 - "Field Functions".
You are welcome.

first you should to define your parameters as a fieldfunktion... right click on fieldfunktion.. choice scalar... than define your Vm as a Value.. for example 0.2.. your radius too... and I think r is our radialcoordinate right?

Use this:

${Vm} * (1-(pow(${RadialCoordinate},2)/pow(${Radius},2)))

CFD2DXY

Thanks. I have values for Vm and radius but I am confused as what to put for the radial coordinate given as the model is a pipe.