1997 Volume 1997 Issue 72 Pages 21-34
A wind tunnel experiment has been performed to investigate turbulence characteristics and organized motions on the flat roof of a high-rise building. Three velocity components were measured with split- fiber probes designed for measuring flows with a high turbulence intensity and separation. Flow patterns on the roof were also studied by means of flow visualization technique with a laser sheet. In the race of flow normal to a face (α=0°), vortices shed at the windward edge generate a low mean velocity and high turbulence near the roof. The longitudinal distance between the vortices is estimated to be 0.6b and their frequency is about Uoh/b, where Uoh is the approaching velocity at the roof height and b is the width of the building. In the case α=45° conical vortices on the roof cause a low mean velocity and high turbulence near the axes of vortices, and a high mean velocity between them. The spectra of three velocity components suggest that high turbulence energies on the roof are not only generated by a high frequency motion corresponding to the vortex shedding at windward edges of the roof, but also by a low frequency motion, which has a period as same as that of Kerman type vortex in the building wake. Vertical profiles of mean and standard deviation of the three velocity components, as well as spectra of them, are presented and compared with those of approaching flow for the two cases.
