Flow visualization of conical vortices on flat roofs with simultaneous surface pressure measurement

Wind tunnel and full-scale pressure studies of flow over low-rise buildings have repeatedly shown that on the roof, the largest mean and peak suction values are observed for taps beneath the conical “delta-wing type” corner vortices that occur for oblique winds. To better understand the flow mechanism which produces these negative pressure coefficients, a flow visualization study of conical vortex behaviour was performed in the wind tunnels of Colorado State University (CSU) and at full scale at Texas Tech University (TTU). The mean position and size of the vortices as a function of wind direction is presented. Pressures were also simultaneously measured beneath the vortex visualization plane in the wind tunnel for the worst case wind directions. These pressure profiles were correlated with the digitally enhanced images of the vortex flow. The greatest suction was found to follow directly beneath the moving vortex core. For smooth flow, the magnitude of the suction beneath the core was seen to vary inversely with the vortex size, but no relationship between vortex size and suction could be seen for turbulent flow.