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

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 6.9×14 to 8.28×15 for the smooth roof and from 6.9×14 to 3.31×15 for rough roofs. The surface of the rough roof had a mean relative roughness of k/D=3.×1−4 to 7.5×1−4 (k is the roughness height). The results indicated that, for a smooth roof, the transition of the separated shear layer occurs in-between R=6.9×14−4.14×15; for rough roofs, the transitional regime is observed at lower Reynolds numbers (in the case of k/D=7.5×1−4, R<1.24×15). 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 9.66×14.