Low Reynolds model in FLUENT
 

I want to modify low Reynolds number model in FLUENT. I am implementing the exact same definition as given in the equations for Re_y, Re_t, f_mu to implement User Defined viscosity for Lam-Bermhorst and Yang-Shih model. But the results are quite different from what I get by using the in-built models in FLUENT.
Any ideas or help?

Thanks