Abstract
Flow-induced vibrations (FIV) can occur when a flexible or flexibly mounted bluff body is exposed to fluid flow. As the flow passes the structure, the shed vortices downstream of the body can produce fluctuating forces on the structure, causing large-amplitude oscillations. FIV is known as a destructive phenomenon causing fatigue damage to engineering structures. Over the past few decades, numerous studies have been conducted on the FIV of a circular cylinder as a canonical geometry. The FIV response of a bluff body is highly sensitive to its cross-sectional geometry as the location of the separation point, which is intricately linked to the vortex-shedding mechanism, is different for each geometry. Previous studies on the FIV of structures with non-circular and asymmetric cross-sections have mainly focused on the flexibly-mounted rigid bodies in flow. However, to fully understand the complex dynamic response of the system in many real-life applications where the structure has a non-circular cross-section, such as iced-covered electrical transmission lines, decks of suspension bridges, tension chains, and the riser that become asymmetric due to corrosion in the water, the structure’s spanwise flexibility should be considered. This research attempts to fill the gap in the literature by doing laboratory measurements to investigate the FIV of flexible bluff bodies with an asymmetric and non-circular cross-section. The two structures studied in this research are (a) a flexible cylinder with a triangular cross-section and (b) a flexible circular cylinder with an attached flexible splitter plate. Among the parameters affecting the FIV response of the system, the role of the angle of attack of the triangular cylinder and the length of the splitter plate is investigated in our study. Findings from this research can leverage our fundamental understanding of the fluid-structure interactions response of the long-span flexible asymmetric structures, with applications in the design of fluidic energy harvesters as well as suppression of unwanted vibrations of systems operating in fluid environments. A series of well-controlled lab experiments have been conducted using water channel tests. Cylinder’s oscillation was captured using a high-speed imaging technique, and the spanwise continuous response was reconstructed using a modal-analysis based technique. The structural response of the system is analyzed in terms of its oscillation amplitude and frequency. Qualitative and quantitative flow field visualizations and measurements have been conducted using Hydrogen Bubble (HB) and the state-of-the-art time-resolved volumetric Particle Tracking Velocimetry(TR-PTV) techniques. Three-dimensional vortex dynamics in the wake of the structure are studied and analyzed using the proper orthogonal decomposition technique. The interaction between structural dynamic response and the vortex-dominated flow field in the wake of the structure leads to a fully coupled fluid-structure interactions response that is investigated in this research.