[JINXING]

Hello,

I am trying to write a UDF for Fluent to define the working fluid viscosity through the pressure and temperature inside control valve.
Using pressure inlet(40bar) and pressure outlet(0) steady simulation method. Before applying UDF, I used constant viscosity to check the model and determined the pressure range inside the simulation domain(-1.4bar, 40bar).
The UDF can be successfully compiled and loaded. After starting calculation, I got error messages.
I tried to set temperature as constant or pressure as constant to check the reliability of UDF. The simulation worked well when the UDF pressure condition was set as constant(real P = 40.). But the same error appeared when the UDF temperature condition was set as constant(real T = 72.).
I also tried to use constant viscosity to get a converged result and then apply UDF, but the same error appeared.
Here is my UDF and error messages:
UDF.PNG
1.PNG
2.PNG
3.PNG
4.PNG
Any help is greatly appreciated.

Thank you!

[JINXING]

Realizable k-e turbulence model, SIMPLEC method

[andrew-c]

Have you validated the values of viscosity that are coming out of your UDF to ensure they are reasonable? You can add a line in your UDF to print the mu when the UDF runs.

It may also be the distinction between gauge and absolute pressure. I'm pretty sure C_P gives you gauge pressure values, whereas i'm guessing your equation for viscosity is based on absolute pressures. You can add your operating pressure to C_P to make it the absolute pressure, this may fix it.

I think there's a command for obtaining the operating pressure during the run too; something like "get_real("operating-pressure") or something similar. You can also just use the value of your operating pressure if you don't plan on changing it frequently.

[LoGaL]

Most probably you are using gauge pressures and not absolute ones like andrew-c is saying.

For which fluid do you need to implement this model ?

[JINXING]

Thank you andrew-c for your reply.

Printing the mu valve is a good method to monitor the equation's reliability.
I solved the error by changing the unit to SI format. I found the UDF can only use the SI unit even though I changed the unit format(pa->bar, K->℃) in Fluent.

Thank you very much for your suggestion.

[JINXING]

Originally Posted by LoGaL

Most probably you are using gauge pressures and not absolute ones like andrew-c is saying.

For which fluid do you need to implement this model ?

Thank you LoGaL for your reply.

I solved the error by changing the unit to SI format used in the equation.
I am studying the fuel(IFO380) flow characteristics inside the control valve of different opening degrees.

Thank you very much for your suggestion.