Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session H29: Aerodynamics: Fluid-Structure Interaction |
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Chair: Mory Gharib, Caltech Room: 2014 |
Monday, November 24, 2014 10:30AM - 10:43AM |
H29.00001: Numerical investigation of a flexible plate in a uniform flow Xi-Yun Lu, Chao Tang The dynamics of a flexible plate in a uniform flow with different flow directions have been studied numerically by an immersed boundary-lattice Boltzmann method for the fluid flow and a finite element method for the plate deformation. A series of distinct states of the plate deformation are identified, including straight, flapping, deflected, and deflected-flapping modes which depend mainly on the bending stiffness of the plate. The effects of the flow direction and the aspect ratio of the plate on dynamics of the fluid-plate system and elastic strain energy of the plate are investigated. The vortical structures around the plate are analyzed to elucidate the correlation of the evolution of vortices with the plate deformation. It is obtained that the flow-induced flapping mode can efficiently produce elastic strain energy for harvesting fluid kinetic energy. The results obtained in this study provide physical insight into the understanding of the mechanisms on the dynamics of the fluid-plate system and the conversion of fluid kinetic energy to elastic strain energy. [Preview Abstract] |
Monday, November 24, 2014 10:43AM - 10:56AM |
H29.00002: Fluid-solid-electric couplings and efficiency of piezoelectric flags Yifan Xia, Sebastien Michelin, Olivier Doare The spontaneous and self-sustained flapping of a flexible plate in an axial flow can be used for energy harvesting applications by placing piezoelectric patches on its surface, that periodically deform with the plate, generating an electrical current. These piezoelectric elements also introduce a feedback of the output circuit on the fluid-solid dynamics and may modify its flapping behavior. To better understand the dynamics of these piezoelectric flags, the resulting energy transfers and their harvesting efficiency, numerical simulations of the fluid-solid-electric problem were carried out using an explicit description of the energy harvesting mechanism and simple output circuits. In the case of purely resistive circuits, a tuning mechanism is identified between the circuit's time scale and the flapping frequency. When the circuit possesses its own dynamics (e.g. inductive/resonant circuits), a lock-in mechanism is observed that leads to an effective control of the flapping frequency by the output circuit over a large range of parameters and a significant increase in the energy harvesting performance of the device. [Preview Abstract] |
Monday, November 24, 2014 10:56AM - 11:09AM |
H29.00003: On the wake dynamics of flapping inverted flags Anvar Gilmanov, Fotis Sotiropoulos, Julia Cosse, Mory Gharib As recently shown experimentally by Kim et al. (\textit{JFM}, 2013), when a flexible flag with a fixed trailing edge (an inverted flag) is exposed to a uniform inflow it can exhibit complex structural response and rich fluid-structure interaction (FSI) dynamics. We employ a new FSI numerical method to carry out large-eddy simulation (LES) of inverted flags in the range where large-amplitude flapping instabilities have been found experimentally. The numerical method integrates the curvilinear immersed boundary (CURVIB) FSI method of Borazjani et al. (\textit{JCP}, 2008) with the thin-shell, rotation-free, finite-element (FE) formulation of Stolarski et al. (\textit{Int. JNME,} 2013) and is able to simulate FSI of flexible thin bodies undergoing oscillations of arbitrarily large amplitude. The dynamic Smagorinsky model is employed for subgrid scale closure and a wall model is employed for reconstructing velocity boundary conditions. Comparisons with the experimental data show that the simulations are able to capture the structural response of the flag with very good accuracy. The computed results are analyzed to elucidate the structure and dynamics of the massively separated, unsteady flow shed off the flag edges. [Preview Abstract] |
Monday, November 24, 2014 11:09AM - 11:22AM |
H29.00004: The Effect of Aspect Ratio and Angle of Attack on the Transition Regions of the Inverted Flag Instability Julia Cosse, John Sader, Boyu Fan, Daegyoum Kim, Mory Gharib The inverted flag instability occurs when a pliable plate is held parallel to a free-stream, with the leading edge free to move and the trailing edge clamped. Large-amplitude flapping is observed across a slim band of non-dimensional wind speeds. This specific boundaries of this flapping band vary greatly, depending on both the aspect ratio and the angle of attack of the plate with respect to the incoming flow. In addition, both periodic and aperiodic flapping modes exist. The frequency of the plate motion was analyzed and was found to be consistent with vortex-induced vibration. [Preview Abstract] |
Monday, November 24, 2014 11:22AM - 11:35AM |
H29.00005: Dynamic Chord-wise Tip Curvature on Flexible Flapping Plates Nathan Martin, Morteza Gharib The aerodynamic characteristics of long rectangular flapping plates are strongly influenced by the interaction between tip and edge vortices. This has led to the development of many tip actuation mechanisms to independently bend or rotate the tip towards the root of the plate in the span-wise direction. In our current work, the influence of dynamically altering the chord-wise curvature of the tip on the generation of aerodynamic forces is investigated; for this case, the two free corners of the flat plate bend towards each other. The parameters of actuation timing, maximum curvature, Reynolds number, flexibility, and tip speed are independently varied to determine their influence. These results will further the fundamental understanding of unsteady aerodynamics. [Preview Abstract] |
Monday, November 24, 2014 11:35AM - 11:48AM |
H29.00006: Free-standing inflatable solar chimney: experiment and theory Peter Vorobieff, Andrea Mammoli, Nima Fathi, Vakhtang Putkaradze Solar chimneys (or solar updraft towers) offer an attractive way to use solar energy for production of baseload power. In a power plant of this type, sunshine heats the air under a wide greenhouse-like roofed collector surrounding the central base of a tall chimney. The heated air drives an updraft flow through the tower, whose energy is harvested with turbines. For a sufficiently large plant of this type, the thermal mass of the heated ground under the collector is sufficient to drive the flow even when the sun is down. The primary challenge in building the solar chimney power plant is the construction of the chimney that generates the updraft, which must be very tall (hundreds of meters for a commercial-sized plant). Here we present a study of an inflatable chimney which is a self-supporting, deformable, free-standing stack of gas-filled tori. The structure is stabilized via a combination of shape, overpressure, and buoyancy. Theoretical considerations suggest that filling the tori with air rather than with a light gas may be advantageous for stability. The chimney shape is optimized for deformation under wind loading. A prototype chimney has demonstrated the viability of the concept, with experimental results in good agreement with theoretical predictions. [Preview Abstract] |
Monday, November 24, 2014 11:48AM - 12:01PM |
H29.00007: Small-Scale Vortical Motions Effected by Aeroelastic Fluttering of a Self-Oscillating Reed in a Channel Flow Sourabh Jha, Pablo Hidalgo, Ari Glezer The formation, shedding, and advection of a hierarchy of small-scale vortical motions effected by an aeroelastically fluttering reed cantilevered across the span of a square channel are investigated experimentally at low (laminar or transitional) Reynolds numbers using high-resolution particle image velocimetry (PIV) and hot-wire anemometry. Formation and advection of vorticity concentrations along the surface of the reed are induced by concave/convex surface undulations associated with structural vibration modes of the reed. These modes lead to alternate time-periodic shedding of CW and CCW vortical structures having cross stream scales that are commensurate with the cross stream amplitude of the reed motion. The evolution of these vortices in the vicinity of the reed is strongly affected by interactions with the wall boundary layers that engender vorticity filaments spanning the entire height of the channel. These reciprocal interactions between the reed and the embossing channel flow leads to the evolution of small scale motions of decreasing scales that is characterized by enhanced dissipation and a distribution of spectral components that are reminiscent of a turbulent flow even at the low Reynolds number of the base flow. Supported by AFOSR. [Preview Abstract] |
Monday, November 24, 2014 12:01PM - 12:14PM |
H29.00008: Flow-induced instabilities of shells of revolution conveying fluid Gary Han Chang In the present work, we study flow-induced instabilities of an axis-symmetric shell of revolution with an arbitrary non-uniform cross-section due to uniform or pulsatile flow. We consider a fully-coupled fluid-structure interaction model, which we solve using a method that combines the Galerkin technique with the boundary element method (BEM). Several modes in the axial direction have been used in the numerical solution and the mode number in the circumferential direction has been chosen as n $=$ 5. As the flow velocity is increased, the system loses its stability through divergence and the shell buckles. We have also conducted experiments on shells of revolution, made of silicon rubber, conveying fluid in order to observe their flow-induced instabilities. Experimental results show that thin shells of revolution conveying fluid lose their stability by divergence with asymmetric mode-shapes, in agreement with our theoretical results. [Preview Abstract] |
Monday, November 24, 2014 12:14PM - 12:27PM |
H29.00009: Flapping Dynamics of an Inverted Flexible Foil in a Uniform Axial Flow Pardha Saradhi Gurugubelli Venkata, Rajeev K. Jaiman This work presents a numerical study on self-induced flapping dynamics of an inverted flexible foil in uniform flow. The inverted foil considered in this study is clamped at the trailing edge and the leading edge is allowed to oscillate. A high-order coupled FSI solver based on CFEI formulation has been used to present the flapping response results for a wide range of nondimensional bending rigidity using a fixed Reynolds number of 1000 and a mass-ratio of 0.1. As a function of bending rigidity four flapping regimes have been discovered: fixed point, inverted limit-cycle oscillation, deflected flapping, and flipped flapping. The inverted foil configuration undergoes flapping motion more readily and experiences very large amplitude oscillations than the conventional foil. A wide variety of vortex wakes with a maximum of 14 vortices per oscillation cycle have been observed. The inverted limit-cycle flapping generate novel 4P$+$6S (14 vortices) and 2P$+$6S (10 vortices) wakes. On the other hand, the flipped flapping regime is characterized by a von K\'{a}rm\'{a}n wake. We also observe that inverted foil can extract 1000 times more energy from the surrounding fluid compared to the conventional foil [Preview Abstract] |
Monday, November 24, 2014 12:27PM - 12:40PM |
H29.00010: Empirical parametric study of fluid-structure interaction at high Reynolds number Grant Dowell, Michael McPhail, Michael Krane, Cengiz Camci An experimental parametric study of a fluid-structure interaction is presented, in order to identify appropriate conditions for in-depth measurements for validation of fully-coupled fluid-structure interaction solvers. The structure is a rigid, square cross-section beam, to which is attached a thin, flexible, rectangular membrane. The rigid beam is mounted perpendicular to the incident flow, and the flexible element is mounted to the rigid element, parallel to the flow direction, so that it interacts with wake of the rigid element. Time-resolved flexible element motion is captured from two directions using high-speed video, for a range of flexible element aspect ratio, stiffness, and Reynolds number based on flow speed and rigid element dimension. Image processing was then used to characterize the frequency and amplitude of flexible element flap and twist modes. [Preview Abstract] |
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