Surface Roughness
If the texture of the model surfaces has a major effect on the results, activate the Consider surface roughness check box. You can then select whether the roughness is taken into account for All model surfaces or applied According to materials.
For the program to determine the turbulent viscosity near the surfaces, the Sand-grain roughness height Ks needs to be specified. You can define the size of the sand grains in the text box or table column for each material. Note that the value is to be entered in meters.
The Roughness constant Cs controls the shape and spacing of the sand grains. This parameter is set as 0.5 by default, assuming a homogeneous distribution. If there is a non-uniform roughness, though, Cs can be increased up to 1.0.