Experimental study on the effect of surface roughness on the characteristics of a plane wall jet

Surface roughness reflects the obstructive effect of surface features on atmospheric turbulence, and is a key factor influencing the characterization of the near-surface wind field. In this study, the method for measuring roughness in the atmospheric boundary layer was introduced to investigate the effect of surface roughness on the wind profile shape and turbulence characteristics of downbursts. Different roughness landforms in nature were simulated by arranging roughness elements with various sizes and distribution densities. Subsequently, wind field experiments of the downburst outflow section were carried out. The results show that roughness has a strong decay effect on streamwise wind speed; as the surface roughness increases, the vertical height corresponding to the maximum wind speed increases. Meanwhile, the turbulence intensity in the inner layer of the wall jet increases significantly, but the turbulence intensity in the outer layer decreases gradually. To address the problem that the existing empirical models of vertical wind profiles for horizontal wind speeds of downburst are unsuitable for all rough landforms, equations for fitting vertical wind profiles for different rough landforms are proposed. In addition, the surface roughness significantly affects the Reynolds stress in the inner layer of the wall jet. The analysis reveals that the wall jet still follows a dimensionless law in high Reynolds number tests with different surface roughness. The study further provides some references for downburst wind loads considering roughness.