Surface Roughness and Reynolds Number Effects on the Aerodynamic Forces and Pressures Acting on a Semicylindrical Roof in Smooth Flow: Fid-Bau Portal

Surface Roughness and Reynolds Number Effects on the Aerodynamic Forces and Pressures Acting on a Semicylindrical Roof in Smooth Flow

Qiu, Ye / Sun, Ying / Wu, Yue / San, Bingbing / Tamura, Yukio

Abstract

The effects of surface roughness and Reynolds number on the characteristics of aerodynamic forces and pressures on a semicylindrical roof have been investigated in a wind tunnel. Simultaneous pressure measurements on smooth and rough roofs were obtained under the smooth flow condition. The Reynolds number, based on the cylinder diameter $D$ , was varied from $6.90 \times 10^{4}$ to $8.28 \times 10^{5}$ for the smooth roof and from $6.90 \times 10^{4}$ to $3.31 \times 10^{5}$ for rough roofs. The surface of the rough roof had a mean relative roughness of $k / D = 3.0 \times 10^{- 4} t o 7.5 \times 10^{- 4}$ ( $k$ is the roughness height). The results indicated that, for a smooth roof, the transition of the separated shear layer occurs in-between $R = 6.90 \times 10^{4} - 4.14 \times 10^{5}$ ; for rough roofs, the transitional regime is observed at lower Reynolds numbers (in the case of $k / D = 7.5 \times 10^{- 4}$ , $R < 1.24 \times 10^{5}$ ). In addition, the mean lift coefficient and the root-mean-square (R.M.S.) pressure coefficient of the rough roofs are considerably lower than those of a smooth roof. It was also found that the surface roughness has a significant influence on the flow around the cylindrical roof. The results of power spectra confirmed that the rough roof presents good organization of vortex shedding; however, no prevailing shedding frequency could be detected for the smooth roof at $R$ beyond $9.66 \times 10^{4}$ .