UDF for turbulence model implementation
 

Hallo,

I have just written a UDF for the AKN model (Abe-Kondoh-Nagano).
I tested it for a channel flow, a backward facing step and a ribbed duct.
Upon reaching a convergent solution with a k-e model with enhanced wall treatment I switch off the calculation of the turbulence transport equations and, after initialization of the UDS, I solve for their transport equations, in order to compute the user-defined turbulent viscosity to use in the momentum equations.

My problem is when I first start with the UDS because I often get AMG solver divergence at the first iteration. So I first set the URF to very low values and solve for each UDS separately and without the momentum equations activated. Then I start increasing the URF and later I activate the flow calculation as well.

I am wondering if someone has the same problem when dealing with UDS for a user defined turbulence model.
Furthermore, when using the AKN model implemented in Fluent I can keep the default URF for momentum, k and e and the calculation converges. Does someone have an explanation for this? (actually Fluent and I should solve the same equations!)

Thank you in advance for your answers.
L.

Hello Luca,

Though this is an old post but were you able to get the solution to the problem. I face similar issue with AKN model.

Thanks