A New Aerodynamic Phenomenon and Its Effects on the Design of Ultra-High Cylindrical Towers

Abstract

The paper presents the discovery – by means of wind tunnel tests and with the support of CFD simulations – of a new aerodynamic phenomenon around circular cylinders. It is a new type of bistable flow, which is induced by the presence of ring beams along the height of a cylinder with a free-end. This investigation was performed within a research project on Solar Updraft Towers, i.e. ultra-high structures (1 km or even more) to produce renewable energy. They convert solar radiation into electric power by using the natural updraft of heated air in a ultra-high chimney. Bistable flows around isolated circular cylinders are known in the critical range of Reynolds number. This new type of bistable flow presents some similarities, but the conditions of occurrence make it original and physically unique. The dependency on the Reynolds number has been investigated in the wind tunnel and in URANS numerical simulations. So far, no reason has been found, which could suggest the disappearance of the phenomenon induced by the spanwise rings in full-scale condition. Therefore, stiffening rings along the height of towers – which are usually regarded as a strategy for reduction of structural vulnerability to the wind action – might become a double-edged sword, especially when the distance between rings is lower than the tower diameter.