New expressions for the surface roughness length and displacement height in the atmospheric boundary layer

An alternative model for the prediction of surface roughness lengthis developed. In the model a new factor is introduced to compensatefor the effects of wake diffusion and interactions between the wakeand roughness obstacles. The experiments are carried out by the useof the hot wire anemometry in the simulated atmospheric boundarylayer in a wind tunnel. Based on the experimental data, a newexpression for the zero-plane displacement height is proposed forthe square arrays of roughness elements, which highlights theinfluence of free-stream speed on the roughness length. It appearsthat the displacement height increases with the wind speed while thesurface roughness length decreases with Reynolds number increasing.It is shown that the calculation results based on the newexpressions are in reasonable agreement with the experimental data.