Development and Verification of a Flow Model of Conical Vortices on Saddle Roofs

Abstract

Through particle image velocimetry, conical vortices were observed near the leading edge of a flat roof and two saddle roofs whose high points were windward. The influences of wind direction and roof curvature on the appearance of conical vortices are discussed in this paper. The results indicated that when the wind direction changed from along the diagonal to deviating from the diagonal of the roofs, the conical vortex close to the approaching flow changed, becoming more oblong. At the same wind direction, a greater roof curvature led to a larger angle between the vortex axis and the leading edge of the saddle roof. Based on velocities measured in conical vortices by flow visualization, a simplified two-dimensional vortex model was established by adding a transitional region between the vortex core and the potential flow region of the Rankine vortex. Through this flow model, the intensities of conical vortices on the two saddle roofs under different wind directions were deduced. The quasi-steady theory was corrected by including the effect of vortices. With this two-dimensional vortex model and the corrected quasi-steady theory, the mean and peak suctions beneath cores of conical vortices on the two saddle roofs were predicted, and these predictions were verified by measured pressures.