UDF, Herschel-Bulkely model don't have Yielding viscosity term
 

Dear All
I would to used Herschel-Bulkely model but my model don't have Yielding Viscosity. Can be any body help me to use model in Fluent for Herschel-Bulkely model only don't have the Yielding Viscosity term. Please, If any body have UDF for Herschel-Bulkely model send me.
Many Thanks for help me
Emad