Search for: All records

Limit-cycle oscillations of bodies with airfoil cross-sections is a subject of keen interest for engineering applications. In systems consisting of multiple such closely spaced bodies, the aerodynamic interactions amongst two or more such bodies can influence the system response. The nature of these interactions is examined with respect to variations in external parameters such as freestream speed and system parameters such as inter-oscillator spacing and the number of airfoil oscillators. By using a co-simulation scheme, which consists of a reduced order three degree-of-freedom piezostructural system and an unsteady vortex lattice method fluid solver, the effects of these parameters on the resulting aerodynamic loads on the system, the overall dynamic response, and the critical flutter speed are studied. In a three-airfoil oscillator system, the effect of the position of the inner airfoil oscillator is extensively studied with a focus on characterizing airfoil interactions and airfoil-wake interactions. For different parallel configurations, studies of bifurcations with respect to different control parameters are conducted. 

With the computational resources becoming available, data-driven methods have emerged as powerful means for equation discovery and model construction. Sparse regression methods such as SINDy (Sparse Identification for Nonlinear Dynamical Systems) can be used for developing reduced-order models of nonlinear systems. In this study, the authors examine how SINDy can be used for developing low-dimensional models for airfoil systems, which experience unsteady aerodynamic loads and flutter instabilities. For a system of multiple closely spaced airfoil oscillators, analytical models are not readily available to determine flutter instabilities, and one has to take recourse to experimental and numerical means. In this work, as a starting point, data collected through simulations of unsteady aerodynamics of a single airfoil oscillator system are considered and a reduced-order model is constructed based on this data. 

Vortex-induced vibrations are oscillatory motions experienced by a body interacting with an external flow. These vibrations can be harnessed for energy harvesting purpose. A cantilever beam with a cylinder attached at the free end represents the bluff body oscillator of interest here. Vortex-induced vibrations of two adjacent bluff-body oscillators are studied by varying the transverse spacing between the oscillators. A finite element model of the system is used to numerically study the associated fluid–structure interactions. For the case with two oscillators, the effect of varying the oscillator spacing on the system response is studied. Dynamic mode decomposition is used for extracting coherent spatio-temporal structures in pressure fields. The system spectral response for the single oscillator and coupled oscillators cases are studied to examine the system dynamics. The obtained numerical results for the system dynamics are found to agree with previously reported experimental results in the literature. The present work can form a basis for constructing computational models of fluid coupled bluff-body oscillators and configuring arrays of bluff-body oscillators for energy harvesting. 

Energy harvesting from flow-induced vibrations has gained substantial attention in the last two decades due to the rising demand for renewable and sustainable energy sources, as well as the widely availability of these sources, offering a viable alternative in areas where other ambient energy sources may not be readily accessible. Flow-induced vibrations of bluff bodies are characterized by complex nonlinear dynamics, for which accurate models are currently lacking. In this work, a circular cylinder attached to the free end of a piezoelastic cantilever is considered for energy harvesting. When placed in a flow, this system undergoes vortex-induced vibrations. A reduced-order model is developed to understand fluid-structure interactions of this system. A wake oscillator has been used to describe vortex-induced vibrations and a finite-element model has been used to model the piezoelastic cantilever. The developed model is used to explore the interplay amongst the fluid, structure, and piezoelectric element. The results obtained are compared to experimental data from literature, in terms of the vibration amplitude, vibration frequency, and power obtained. Modifications to the wake oscillator model are examined to better reflect the fluid-structure interactions. It is found that there is a trade-off between accurately predicting the vibration amplitude and accurately predicting the vibration frequency.