Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session S14: FSI: Energy and Propulsion |
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Chair: Patrick Musgrave, US Naval Research Laboratory Room: 307/308 |
Tuesday, November 26, 2019 10:31AM - 10:44AM |
S14.00001: Fluid-Structure Interactions of Structure-Borne Traveling Waves Patrick Musgrave, Austin Phoenix Structure-Borne Traveling Waves (SBTWs) are a promising means of underwater propulsion, but the coupled fluid-structural dynamics are poorly understood. SBTWs operate by taking advantage of a structure's inherent modal properties (mode shapes and natural frequencies). This enables traveling wave generation using two actuation points instead of requiring a large array of actuators. However, the fundamental reliance of SBTWs on structural properties also introduces coupling with the surrounding fluid. This study extends SBTW generation to underwater and accounts for the two-way coupled, fluid-structure interactions. SBTWs are analytically and experimentally generated on a slender, cantilever beam in a quiescent fluid. An analytic model is developed coupling a linear Euler-Bernoulli beam with a potential flow solution for the surrounding fluid. The structural response is solved via a Galerkin-type solution. SBTWs are then generated by applying multi-input forcing to the coupled system. The model is experimentally validated against a cantilever beam in quiescent water. Experimental SBTWs are generated using flush-mounted piezoelectric actuators and the structural response measured using non-contact scanning laser vibrometry. Analytic and experimental SBTWs are compared at several frequencies and with varying waveforms (i.e. wavelength and wave speed). The results demonstrate that SBTWs can be generated in water and the fluid-structure interactions accurately captured. [Preview Abstract] |
Tuesday, November 26, 2019 10:44AM - 10:57AM |
S14.00002: Fluid-Structure Simulations of a Flexible Heaving Airfoil Jonathan Cappola, David MacPhee Motivated by experimental studies in biomimetic propulsion, a computational framework is used to simulate the heaving of a two-dimensional NACA airfoil with chordwise flexibility. A strongly-coupled fluid-structure interaction solver is developed using finite-strain solid deformation and a translating reference frame within the OpenFOAM framework. Using this model, we investigate any possible performance improvements of a flexible airfoil over the rigid in varying oscillating frequency and material elastic modulus. Flow structures and stress configurations are analyzed and discussed as related to simulated thrust and lift enhancements. [Preview Abstract] |
Tuesday, November 26, 2019 10:57AM - 11:10AM |
S14.00003: Numerical and Experimental Investigation of Oscillating Flexible Foils with Application in Energy Harvesting Kiana Kamrani Fard, Penglei Ma, Michael Prier, James Liburdy The effect of relative leading edge motion of a flapping airfoil in energy harvesting regime is studied in reduced frequencies of k $=$ fc/U $=$ 0.06 -- 0.14, pitching amplitude of $\theta \quad =$ 70\textdegree and heaving amplitude of h0/c $=$ 0.5. A low order discrete vortex model with a vortex shedding criterion at the leading edge is used to estimate the transient lift force and the results are compared to 2-D CFD and direct force measurements via load cell. Positive leading edge motions in which the leading edge rotates in the same direction as the pitch angle and reduces effective angle of attack, are shown to improve the heaving power coefficient and efficiency compared to the rigid case by shifting the primary peak later in the stroke where the heaving velocity is higher. Whereas negative leading edge motions, in which the leading edge rotates in the opposite direction as the pitch angle and increases effective angle of attack, are shown to negatively influence the heaving power coefficient and efficiency compared to the rigid case, by reducing the primary peaks. [Preview Abstract] |
Tuesday, November 26, 2019 11:10AM - 11:23AM |
S14.00004: An Alternative Geometry for a Galloping Energy Harvester Sam Tucker Harvey, Petr Denissenko, Igor Khovanov Interest in aeroelastic energy harvesters has grown substantially in recent years due to their potential for low maintenance and low cost energy solutions, particularly with regard to autonomous electrical devices, such as wireless sensors. The development of aeroelastic energy harvesters to date has focused mainly on the flutter of airfoils, the galloping of prismatic structures and vortex induced vibrations as a means to generate energy. In this work an alternative geometry for a galloping energy harvester, initially inspired by the trembling of aspen leaves in barely noticeable flows, is investigated in two alternative configurations. The dynamics of a prototype device have been characterised experimentally with the use of a motion tracking system, while the flow patterns generated around the device have been evaluated by smoke wire visualisation and particle image velocimetry (PIV). In the second configuration the presence of a leading edge vortex is found to coincide with higher potential energy harvesting performance. The interaction of multiple harvesters within the flow field is also demonstrated to result in phase locking synchronisation. [Preview Abstract] |
Tuesday, November 26, 2019 11:23AM - 11:36AM |
S14.00005: Unsteady loads mitigation using flexible wings Gabriele Pisetta, Ignazio Maria Viola In nature, fluid flows are inherently unsteady, and any wing-like device immersed in them experiences loads fluctuations. In some cases, these fluctuations may result in fatigue failures, and thus they strongly affect the reliability of the whole device. An effective control strategy would consist in a passive device capable of applying fast, local control action. This can be achieved using a flexible structure. In this presentation, we consider the loads on a tidal turbine operating in a shear flow, and we introduce a novel blade design to reduce the load fluctuations. We show that a blade with a flexible trailing edge can mitigate the fluctuations of the blade root bending moment, without affecting the mean torque, and thus the power generated by the turbine. Using a numerical method based on the seminal work of Theodorsen, we model the foils’ flexibility as a torsional spring, and we perform a parametric study to identify the optimal spring parameters. The dynamic analysis of the system shows that the fluctuations of the root bending moment can be reduced by $93\%$. Our results prove the potential of a flexible structure to alleviate the loads fluctuations arising on a wing in an unsteady flow, and they underpin the development of more sophisticated models of flexible wings. [Preview Abstract] |
Tuesday, November 26, 2019 11:36AM - 11:49AM |
S14.00006: A numerical study of a vertical axis turbine with chordwise-flexible blades operating at low tip speed ratios Pierre-Olivier Descoteaux, Mathieu Olivier This talk will present high-fidelity numerical simulations allowing the performance evaluation of a Vertical-Axis Turbine (VAT) equipped with chordwise-flexible blades. The simulations are carried out with a partitioned Fluid-Structure Interaction (FSI) code in which an in-house structural finite-element solver is linked to a finite-volume flow solver based on the OpenFOAM library. The idea behind this study is to take advantage of the strongly changing flow conditions acting on the blades when the VAT operates at low tip speed ratios. In such cases, the unsteadiness of flow forces can be used to alter the shape of the blade. This analysis will show under which conditions it is possible to increase the efficiency of a VAT by allowing passive foil deformations at a high Reynolds number. The FSI effects related to the flexibility and inertia of the blade will be investigated and the mechanisms that allow efficiency improvements, such as stall mitigation, will be described and compared against rigid-blade VAT operating in the same regime. [Preview Abstract] |
Tuesday, November 26, 2019 11:49AM - 12:02PM |
S14.00007: Fully-resolved wave-structure interaction simulations of a two-dimensional submerged point absorber with three degrees of freedom~ Panagiotis Dafnakis, Amneet Pal Bhalla, Giuliana Mattiazzo, Giovanni Bracco A fully-resolved wave structure interaction (WSI) framework is developed to simulate a submerged point absorber. The WSI model is based on the fictitious domain Brinkman penalization method in which the solid body is treated as a porous body of vanishing permeability. For validating the model, forced damped-oscillation of a cylinder in various damping regimes along with several grid convergence studies are performed. The WSI model is~compared against Cummins equation based Simulink model to demonstrate the differences between the potential flow theory and the nonlinear Navier-Stokes based methodologies. Time domain simulations are carried out for one, two, and three degrees of freedom buoy in order to analyze the surge, heave and pitching motion of the device using two methods. Furthermore, the WSI model is used to calculate the conversion efficiency of the point absorber for various wave and device parameters. [Preview Abstract] |
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