Non-stationary winds effects over large partially-open roofs: A CFD study regarding the role of unsteady aerodynamics

Non -stationary winds are increasingly attracting the attention of the scientific community and, despite not being explicitly considered in current design practice, they are known to produce important damages. In particular, the non-stationarity of such events has important consequences with respect to four main aspects which affect the definition of design wind loads: (i) the design wind speed definition, (ii) the wind profiles, (iii) the calculation of the structural response and (iv) the insurgence of unsteady aerodynamics effects. While the first three aspects already received considerable attention, the last one is still largely unclear and its relevance still to be assessed. In particular, for non -stationary winds such as macro- and micro-downbursts, the ramp -up time might become so short to trigger unsteady aerodynamic effects in the overall flow arrangement, which cannot be inferred from results obtained for stationary cases. In this paper, we propose a first investigation of such matter considering a large stadium roof using Large Eddy Simulations. Results show that, for the considered case, noticeable unsteady aerodynamic effects, which leads to an amplification of wind loads, can be triggered when the wind rump -up time is in the order of 30 s, and quickly decrease in importance for higher rump -up times.