Horizontally homogeneous/constant in empty computational domain

Using SimScale Fluid Flow / CFD
1

According to Blocken (https://pure.tue.nl/ws/files/7993534/687442152079717.pdf, section 5.7) one needs to check if one’s empty computational domain (but using the correct roughnes length [inlet) and roughness height [for ground wall]) is horizontally homogeneous/constant.
I don’t know if it has to be homogeneous/constant in speed and turbulant kinetic energy, but I assume minimally for the speed. Correct?

So I did some experiments in SIMSCALE using an empty EFV,; using an inlet logarithmic ABL of z0=0.03m with:

  1. a ground wall with wall roughness of ks=0.33m (=10.9*z0) and Cs=0.9:
    https://www.simscale.com/workbench/?pid=5399799295123716855&mi=run%3A220%2Csimulation%3A134&mt=SIMULATION_RUN
    or
  2. a ground wall without wall roughness:
    https://www.simscale.com/workbench/?pid=5399799295123716855&mi=run%3A222%2Csimulation%3A134&mt=SIMULATION_RUN

One would assume that the wall with explicit roughness height (equivalent wih z0) would have the most constant speed over the 165m, but infact the wall without roughness is slightly more constant (see the related Solution Fields and the deviation of the z=9m line).

In both cases the plot of the turbulent kinetic energy is certainly not constant.

So my questions are:

  • do both speed and turbulent kinetic energy need to be constant over the whole length?
  • or did I make somewhere an error in defining my EFV and/or its parameters?
  • or do I define ‘constant’ too strict?
  • why is turbulent kinetic energy so depending on distance (in both a wall with roughness height and/or without it)?

I hope someone can help me.

Thanks.

All the best,

Victor

2

Is there someone who has some idea on this? I understand it is one of the important test to verify that the CFD simulation can be ok, so I hope someone can help me.
Thanks.

All the best,

Victor