On the Interaction between vortex-induced vibrations and galloping in rectangular cylinders of low side ratio

The thesis deals with the interaction between vortex-induced vibrations (VIV) and galloping for rectangular cylinders of low side ratio, which is defined as the body width on the body depth facing the fluid flow (SR=B/D). In particular, the interaction mechanism has been characterized for a wide range of Reynolds numbers (Re) and mass ratios (m*), aiming to provide a complete description of the response in several flow situations (smooth and turbulent, air and water) for bodies which exhibited, or were known to have, a pronounced proneness to this type of instability. This type of flow-induced vibrations phenomenon occurs for particular combinations of both aerodynamic and dynamic characteristics of a system. The study consists in two main parts, both of them aimed at proposing a complete framework for scientific and designing purposes. The first one investigates the phenomenon occurring in sectional models purposely designed and experimentally tested, whereas the second one is devoted to the implementation of a predictive model for the interaction, implying also further experimental measures to assess the model key-parameter. Several sectional models of a SR=1.5 have been tested given that this section demonstrated to be particularly prone to the interaction between VIV and galloping. Nevertheless, the majority of former literature investigations were performed on the square section. The response features of such a phenomenon are still not fully understood. In order to have a deeper insight and to give a complete description of the interaction, the present investigation was conducted focusing particularly on the SR=1.5 rectangular section: this is a soft oscillator respect to the incipient instability, while the same rotated section with an angle of attack of 90°, that is SR=0.67, is generally referred to as a hard-type one. Results in air flow showed peculiar amplitude response curves differently shaped depending on Re, m* and corners sharpness accuracy. Results in water flow showed the response in amplitude and frequency to be strongly influenced by the abrupt change of m*, recalling the different responses in air and water flow regime reported in literature for a circular cylinder, though related to VIV only. SR=0.67 shows a completely different response, although remaining, differently from air flow measurements, a soft oscillator. Further tests on m* variation constituted an integration for the data so far available in literature about these sections.