Application Of Wind Fairings Forsuper-tall Building Aerodynamic Optimization

Aerodynamic optimization plays a prominent role in wind resistant building design. Corner chamfering, tapering, twisting, and having openings at upper portion of the structure are commonly adapted approaches of building aerodynamic optimizations. However,these approaches, if adapted,will alter a building's geometry and appearance permanently from its original design, which may cause inconsistence with the original architect's design concept, loss of usable space and difficulties in the course of design and construction. As such, these approaches are hardly accepted in design communities. Based on wind-adaptable design concept, this paper has proposed a new approach of building aerodynamic optimization by utilizing wind fairings. For most of the time, wind fairings are tucked into the building and invisible when the building is operating under normal wind conditions. During strong winds, carefully designed wind fairings will be put into use to enhance resilience of the building to wind effects. This study investigated various types of fairings and selected two typical types of them (Scheme I,Scheme II) for wind tunnel testing to quantitatively assess their effectiveness. The major research contents and results are as follows:To begin with, the concept of wind-adaptable design by using of wind fairings as flow control devices is discussed. When a severe wind storm is in forecast, the building's flow control devices, wind fairings,are launched to transform the building from its base shape to an aerodynamically optimized shape to enhance the building resilience to the windstorm. When the windstorm ends, wind fairings will be tucked back into the building, becoming invisible from outside. The building will be back to the base shape as the architect designed originally. And this paper suggests that applicable wind fairings for buildings have to meet the following requirements: operable, suitable and omnidirectional.A series of force-balance tests were carried out in the boundary layer wind tunnel of Zhejiang University to measure the aerodynamic forces of a high-rise building model with and without wind fairings to study the influence caused by wind fairings. Furthermore, optimizing size of the wind fairings to further enhance their effectiveness was studied. All the models were based on a high-rise building model with square section and with the aspect ratio of 6:1. The model with no fairings was first tested as the reference,and then tested with different sizes of fairings being installed for comparison. In general, wind-fairings were found reducing the across-wind overturning moments with little influence on along-wind loads. And detailed parameter studies showed that the effectiveness of wind fairings is sensitive to their geometric dimensions. The effectiveness was drastically reduced when wind fairings were either oversized or undersized. With appropriate sized wind fairings, it could reach a reduction of 20% in the across-wind overturning moments of a building. Roughly speaking, it was found that for Scheme I fairings, the optimal wind fairings should have a relative width of about 1/10 of the building dimension, a relative height of 1/5 of the building dimension or more and a fairing opening angle of about 45°. For Scheme ? fairings,the optimal dimensions consisted of a relative width of about 1/10 and a relative gap of about 1/10.2D numerical simulation was conducted in the comparative study between the Scheme ? and the square section. Through comparing the time-history of dynamic coefficients and flow patterns, Scheme ?were found to reduce both the amplitude of lift force and the static drag force. Consistent with the result of HFFB test, the reduction was enhanced with the increasing of the width of fairings. Similarly, the optimal dimension was found to have a relative width of about 1/10. In addition, the flow separation was found less significant with fairings in place compared to the square section, which is likely to be the reason of the reduction of dynamic forces.Pendulum-type aeroelastic model tests were carried out in the wind tunnel to further validate the effectiveness of wind fairings and also to investigate the effects of various aspect ratios. Throughout the tested configurations, it was noticed that the reduction of cross-wind overturning moments due to fairings tended to be more substantial at high reduced speeds than at a lower reduced speed. The Scheme ? was found more effective than Scheme ?, and in some cases, a reduction of 30 % on cross-wind overturning moments could be achieved. Along-wind loads were found to have been little influenced or slightly reduced by wind fairings.