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K (turbulent kinetic energy) ground(wall) BC

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Old   May 18, 2017, 05:41
Question K (turbulent kinetic energy) ground(wall) BC
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I am working on a simulation of wind on buildings.
I am using a RASModel kEspilon with the simpleFoam solver.
I am applying ABL (atmospheric boundary layer) conditions.

for the "ground" patch of my domain the boundary condition of K is KqRWallFunction, but I am not sure which value should I use. in most of the tutorials they apply the same value as the internal field but in the turbineSiting tutorial they applied uniform 0.

so for the K on the ground patch should I apply
KqRWallFunction - value: uniform 0
KqRWallFunction - value: same as internalField

thank you for your help.
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Old   May 19, 2017, 04:31
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For the value for a derived boundary condition (such as wall functions) usually the value entry is only a placeholder. It may get used in the first iteration if some value is needed, but usually a value will be set as soon as the boundary condition is updated. This means most of the time as long as the value is physical it does not matter too much what this value is. There may be some rare cases where there is an influence, but I would not know one by heart.

In your case I would use the internalField value, but I doubt you will find much difference if you use 0.

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Old   May 23, 2017, 03:28
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thank you Tom for your help. now I understand how it works.
for information, I did 2 simulations with different initial K conditions (as stated in post #1) and obtained the same results.

Best Regards
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abl flow, boundary condition, building aerodynamics, turbulent kinetic energy, wall boundary condition

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