Strong suction events during reformation of leading-edge vortices on building side walls

Pressure measurements on the side walls of the Silsoe 6 m Cube exhibited minimum pressure coefficients which were significantly lower than expected from quasi-steady theory. Both velocity and pressure data are used to illustrated that this can be associated with the reformation of the Leading-Edge Vortex (LEV) as the wind direction changes. Velocity data at mid-height showed the progressive reversal of flow direction as the LEV grew, with the strongest reversed flows occurring at the more windward location for a short duration with a magnitude more than twice that which might be expected from the mean observations. Similarly, the pressures exhibited a pattern of sequential increase in suction as the LEV developed, with the highest peak usually occurring at the windward tap. Pressures from two of the taps on the windward face are used to provide a local estimate of the wind dynamic pressure and wind direction, since reference data from a remote mast fails to give sufficiently accurate information to relate to short duration events. Conditional averaging is used to highlight the underlying patterns associate with the pressure spikes. This shows a clear pattern of strong suctions occurring near the windward edge and then weakening as the LEV develops and spreads across the face of the sidewall.