I cann't understand the description in Fluent's user's guide.How does it combine the two-layer model with the enhanced wall functions?Is it just as the combination of the standard k-epsilon model with the standard wall functions?

I think it just like the combination of the standard k-epsilon model with the standard wall functions

Aha!Thank you!

Enhanced wall treatment is treatment right down to the surface using the turbulence model (K-E) needing a mesh y+ of 1 or so, but wall functions uses emphirical-type substitutions (emphirical meaning experimental generic stuff), the actual wall function model used is lauder-spalding I think and needs a y+ of 30-60.