Prandtl Mixing length Vs. Isotropic turbulent

Mohammad Kermani

Hi:

Prandtl Mixing length hypthesis recommends that:

u' ~= v' ~= l*du/dy throughout the whole flow field.

The condition u' ~= v' is the definition of isotropic at a point.

Now the question is: How prandtle mixing length hypothesis, which is the basis for all the zero equation models, can justify the anisotropicicty of turbulent colse to the wall?

Thanks for your comments.

MJ