Leading Edge Vortex Dynamics on a Flat Roof

Abstract

Roof pressure data from the field testing (Full-Scale) of the Silsoe 6m Cube, for conditions when the wind is nearly perpendicular to one of the vertical faces, has been observed to exhibit occasional, but random in time, high suction pressures on the windward half of the roof. Conditional averaging of data from a number of taps reveals a systematic pattern affecting many points on the roof. Model scale data obtained with a 1:40 scale model in the University of Auckland Boundary Layer Wind Tunnel and with a 1:5 scale model in Florida International Uni-versity’s Wall of Wind (WoW) facility is shown to give very similar event patterns. It is revealed that all of these patterns are essentially the same when expressed in non-dimensional form nor-malised using parameter related to conditions around the time of the events. Computational Fluid Dynamic (CFD) modelling of the flow over the cube using Large Eddy Simulation also gives a similar pattern of pressures and illustrates the manner in which a strong leading edge vortex is formed and expands to cover most of the roof, displacing the resident vortex associated with the background separating-reattaching flow ahead of it. The data from the Wall of Wind is used to illustrate that the pattern has a band of relatively high pressures spreading across the entire width which moves ahead of the suction wave.