Flow Dynamics and Aeroacoustics of Flow-induced Vibration of Bluff Bodies

Flow-induced vibration (FIV), a common phenomenon of fluid-structure interaction (FSI), is found everywhere and at all scales in the applications of marine, civil, aeronautical, and power engineering. The study of FIV phenomenology, ranging from fatigue and concomitant damage of structures to its exploitation for energy extraction, has been an active area of fundamental research. The research on the mechanism supporting the amplifying, stabilizing, and suppressing of FIV has practical implications for the structural design for optimal engineering fatigue control, energy utilization, etc. Moreover, the noise propagation generated from FIV is also accompanying environmental pollution that should not be ignored. However, past research on the FIV supported by nonlinear spring and the corresponding detailed FSI characteristics are limited. The present study will conduct a numerical FIV study of bluff bodies mounted by linear and nonlinear springs, and analyze the impact of stiffness nonlinearity on the FIV responses, including the amplitude variation, phase change, frequency variation, and wake pattern. The technical method used in this part is direct Computational Fluid Dynamics/Computational Structural Dynamics (CFD/CSD) simulation with the full-order model (FOM), via the coupled Navier-Stokes and body-structure equations. Additionally, the present study investigates the geometrical influences on FIV response and the mechanism underpinning the transfer from lock-in range to desynchronization or galloping range. Different body shapes, varied Reynolds numbers, and reduced velocity will involve many cases, as a result, expensive time will be consumed if the corresponding grids are generated and FOM calculations are carried out for each case. This part of the research will be mainly based on the data-driven stability analysis using the reduced-order model (ROM), and FOM based on CFD/CSD method will be used as supplementary for comparison. ROM could also provide the modal analysis and physical perspective that are not available for FOM. Combining ROM and FOM methods, this thesis explores the mode transformation and interaction in the lock-in behavior of laminar flow past a circular cylinder. For the galloping analysis, it is observed very small changes in the windward interior angle of an isosceles-trapezoidal body can provoke or suppress galloping---indeed, a small decrease or increase (low to 1°) of the windward interior angle from a right angle (90°) can result in a significant enhancement and complete suppression, respectively, of the galloping oscillations. This supports our hypothesis that the contraction and/or expansion of the cross-section in the streamline direction is significantly responsible for the galloping response. Furthermore, one novel methodology of data-driven stability analysis via the superposition of 2-D reduced-order modes (SROM) for the purpose of performing modal analysis and stability predictions of 3-D flow-induced vibration with spanwise shear inflow is presented. Lastly, noise propagation from energy harvesters based on the FIV mechanism also deserves attention. Owing that there is limited past research on noise propagation from oscillating cylinders, an investigation on aeroacoustics study of different oscillation patterns of single cylinder and tandem cylinders is carried out