Attenuation of the unsteady loading on a high-rise building using active control

Abstract

The present work numerically investigates the 3D flow structures around a canonical high-rise building immersed in an atmospheric boundary layer at different oncoming wind angles, using wall-resolved large eddy simulations. The switching between two vortex shedding modes is explored, and the influence of the atmospheric boundary layer on suppressing symmetric vortex shedding is identified. It is shown that the antisymmetric vortex shedding mode is prevalent in the near wake behind the building, with strong coherence between the periodic fluctuations of the building side force and the antisymmetric vortex shedding mode demonstrated. Exploiting this idea, active flow control strategies are designed to alleviate the aerodynamic side-force fluctuations.

Two feedback control strategies are then developed to attenuate the building’s unsteady loading when the oncoming flow is normal to the wider side of the building, using pressure sensing on just a single building wall. The sensor response to synthetic jet actuation along the two ‘leading edges’ of the building is characterised using system identification. Both the designed linear controller and the least mean square adaptive controller attenuate successfully the side-force fluctuations when implemented in simulations. The linear controller exhibits better performance, and its effect on the flow field is to delay the formation of dominant vortices and increase the extent of the recirculation region.

Motivated by the effect of the downwash flow on the near wake of the building, an open-loop active control in the form of a synthetic jet located on the top surface is then considered. The aim is again to suppress side force fluctuations, this time exploring whether the simpler control setup can be effective across a wide range of oncoming wind angles. The behaviour of the synthetic jet and its effect on the building’s unsteady side force, time-averaged flow fields and unsteady flow structures are investigated numerically. The synthetic jet actuation is found to reduce the side-force fluctuation of the building, enhance the downwash flow and successfully attenuate the antisymmetric vortex shedding.

Finally, the possibility of using a robust feedback control strategy mitigating the unsteady loading of a high-rise building exposed to differing oncoming wind directions is explored. A reference linear open-loop transfer function is identified, and the differences between the reference open-loop system and open-loop transfer functions for different oncoming wind angles are assessed by v-gap. An H loop-shaping feedback controller is then designed and achieves the attenuation of the building’s side-force fluctuations for differing oncoming wind angles.

This work can provide a theoretical basis for the practical application of novel active control approaches to attenuating the side-force fluctuation of the high-rise building exposed to differing oncoming wind directions.