Dynamics of Bluff Bodies with Internal Nonlinear Oscillators: Vortex-Induced Vibration Suppression, Partial Wake Stabilization, and Drag Reduction

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Fluid-structure interaction is ubiquitous across a range of engineering applications, from flutter and divergence in aerodynamics, to vibration of fuel rods in nuclear power reactors, tension legs in offshore platforms, wind turbine towers, and hydrokinetic energy harvesting. A major aim of this work is to demonstrate that using intentionally designed nonlinear oscillators inside a bluff body it is possible to passively suppress vortex induced vibrations - VIVs, partially stabilize the wake past the body, and reduce the drag force exerted by the surrounding fluid without any external modification. This research can have broad and significant impact in diverse fields. For example, the reduction of the drag forces on a bluff body through the action of internal nonlinear oscillators might significantly affect the design of future air vehicles and boats by enhancing their performance, enlarging their range of operation and decreasing fuel consumption. Also, enhanced and economical hydrodynamic vibration energy harvesting could be achieved by appropriate design and optimization of internal nonlinear oscillators inside a body undergoing VIVs.In this research, the dynamic interactions of a strongly nonlinear finite-dimensional oscillator with an infinite-dimensional fluid flow will be studied. This is important in understanding not only fluid-structure interaction in a variety of contexts, but also, in a broader sense, because it serves as a testbed for understanding the nonlinear dynamical behavior of a variety of other mechanical (and nonmechanical) systems involving nonlinear interactions of coupled finite- and infinite-dimensional parts. The fundamental importance of dealing with an intermediate-to-high range of Reynolds number -- Re -- lies in the fact that our preliminary results show that the dimension of the attractor in the two-dimensional laminar case is less than four, while in the turbulent case, it is expected to grow as Re to the 9/4 power. This system thus provides a unique opportunity to understand the dynamics of fluid-structure interaction, where the dimension of the attractor varies from one (for periodic response) to much larger values. We will also study the heretofore unexplored role of angular momentum in VIV. Finally, the capacity of strongly nonlinear internal oscillating elements to drastically modify the wake of a bluff body and reduce its drag coefficient at both intermediate and higher Re will be explored. The research will be performed using slow/fast dynamical decompositions, invariant slow manifold considerations, nonlinear system identification, and reduced-order modeling techniques. High-fidelity fluid-structure interaction computations will be performed in the laminar, transition, and turbulent regimes.