Fluctuating pressures on models of tall buildings

Abstract

The objectives of this study have been to explore the high peak suctions developed on building models and their relationship with building shape and the characteristics of the oncoming simulated atmospheric shear flow. The mechanisms causing high suctions were studied first by observing the patterns of the high peak occurrences for various model geometries, orientations and flow simulations, and then by investigating the relationship of the largest peaks with nearby pressures and with the oncoming flow, using a conditional sampling technique. This technique allowed simultaneous time histories to be recorded at 16 locations for a time period centred on the occurrence of an interesting peak at a specified location. The model geometry did not strongly influence the magnitude and location of the most severe values of the observed peaks, although it did alter the most important wind directions. In contrast, the structure of the peak suctions were strongly influenced by the simulated terrain. In the least turbulent flow simulation, the pressure records obtained by the conditional sampling technique over the side face of the building model most nearly parallel to the flow reveal distinct periodicity associated with vortex shedding at the Strouhal frequency. Furthermore, the peak event always coincides with a vortex shedding peak. An increase in turbulence intensity, associated with a more builtup terrain simulation, deteriorates the periodicity of vortex shedding, but the peak relationship with the remaining randomized vortex shedding appears to be maintained. By extending the conditional sampling technique to include simultaneous multi-point pressure and velocity measurements, it was found that negative pressure peaks near the trailing edge of the side face most nearly parallel with the flow are associated with lateral fluctuations of the velocity vector in the approach flow. The intermittent reattachment of the shear layer, along with occurrence of the high suction at the trailing edge as a consequence, appears to be associated with an oncoming flow shift induced by the vortex which sheds from the opposite leading corner.