Kinetic energy profile for ABL over an empty domain with rough surface
 

Dears,
I'm trying to simulate dust drifting from sowing machine using ANSYS-CFX. Before I put the machine and defining the dusts first I have to check the homogeneity of velocity profile, turbulence kinetic energy profile and turbulence eddy dissipation/frequency profile in an empty domain(a big box).
For the empty domain I did sensitivity analysis with k-epsilon and SST k-omega models. From literature and CFD online forums I read SST k-w is better since it combines both k-e(for far from the wall/fully turbulent) and k-w(for near to wall). The bottom boundary of the empty domain is a ground with rough surface. I use the loglaw @ inlet boundary assuming a constant shear stress with height according to Richards & Hoxey, 1993.
Inlet=atmospheric boundary layer
Outlet=zero pressure
Sides=symmetry
Top= opening
Bottom=wall/no slip with rough surface
But the turbulence kinetic energy profile for all cases is by far not homogeneous across the length of the domain.
I really need idea/suggestion,.....
Thanks,