Experimental study of the influence of roughness area density and surface pattern on near wall flow and surface pressure

Abstract

In this study, we built a series of roughness surfaces in an atmospheric boundary layer (ABL) wind tunnel with the aim of determining the characteristics of flow and surface pressure around a rough surface placed on a deep turbulent boundary layer. The ABL has a significant role in the exchange and transfer of momentum close to the wall. In particular, the roughness sublayer (RS), the lower part of the ABL, is two times thicker than the average building height in an urban area. Therefore, it is thought that the thickness of the RS and urban canopy layer has a dominant effect in the formation of the typical characteristics of a fully developed turbulent boundary flow, such as mean and turbulent statistics. This study focuses on the measurement and understanding of the near wall flow and pressure distribution around the roughness. In addition, the roughness area density and pattern were used in three cases for area density (defined as total plan area of roughness surface/total area) such as 25%, 17%, and 11%, and two cases for roughness patterns, i.e. staggered and aligned. Consequently, the RS height was estimated to be approximately 1.8–2.2 H of the roughness height. The surface pressure in the front face becomes lower as the area density increases, whereas the pressure on the back remains almost constant regardless of area density. In addition, the surface pressure at top face becomes higher as the area density increases.