Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session F14: Aerodynamics: Fluid Structure Interaction I |
Hide Abstracts |
Chair: Amir Danesh-Yazdi, Rose-Hulman Institute of Technology Room: Georgia World Congress Center B301 |
Monday, November 19, 2018 8:00AM - 8:13AM |
F14.00001: Aeroelastic Flutter of Wings: Flow Physics, Scaling Laws and Bifurcation Regimes Karthik Menon, Rajat Mittal Aeroelastic flutter is a problem that is relevant in a wide variety of fields, both due to its detrimental effects as well as its possible utility in applications such as energy harvesting. Aeroelastically mounted airfoils exhibit response regimes that are quite different, and often more complex than flow-induced vibration of bluff bodies. Hence, there is a need for novel tools to aid in the modelling and analysis of this phenomenon. In this work, we report on high-fidelity flow modelling of pitching airfoils using a flow solver that is based on a sharp-interface immersed boundary method. A two-way coupled aeroelastic model of a pitching airfoil is used to demonstrate a variety of response regimes. We examine the effect of various parameters, such as spring stiffness and elastic axis location, on the resulting dynamical response. We extract scaling laws based on the flow physics that predict the onset of flutter, and energy maps are used to gain insights into the various bifurcation regimes exhibited by the system. |
Monday, November 19, 2018 8:13AM - 8:26AM |
F14.00002: Flow-Induced Flutter for Enhanced Mixing at Inertial Microscales Aaron Rips, Rajat Mittal Scalar mixing in a channel enhanced by a flag undergoing flow-induced flutter has been investigated using two-dimensional, fully-coupled fluid-structure interaction (FSI) simulations. We find that the addition of a self-oscillating flag in a scalar mixer at inertial-scale Reynolds numbers (50<Re<200) leads to significant enhancement in mixing with a relatively low associated head loss. We examine the sensitivity of the system to both Reynolds and Schmidt numbers to better understand the impact of the flapping on the mixing performance, and to assess the relative importance of advection and diffusion in the mixing process. Large amplitude flutter occurs over the entire range of Reynolds numbers studied and leads to persistent vortices that generate significant cross-stream advection and stretching of the interfaces, across which, diffusive mixing can occur. Finally, we compare the mixing performance of the flags to that due to vortex shedding from a cylinder; this serves as an analog for more conventional passive mixers in the inertial microfluidic regime. Our simulations show that flutter enhanced mixing offers mixing performance that significantly exceeds that of passive mixers but without the attendant design complexity of active mixers. |
Monday, November 19, 2018 8:26AM - 8:39AM |
F14.00003: Application of Recurrent Neural Networks to Wind Speed Prediction from Flapping Flags Jennifer L. Cardona, John O. Dabiri |
Monday, November 19, 2018 8:39AM - 8:52AM |
F14.00004: Abstract Withdrawn Flag flutter is a canonical instability example of flexible Fluid Structure Interaction which has received a strong attention in the last two decades. In this study, we address the stability of an infinitely long two-dimensional flag in a uniform flow and parallel to a free surface. The objectives are to assess the effects of the free surface on flag flutter thresholds and the possible occurrence of free surface-induced instabilities. It will be shown using potential incompressible flow coupled to an Euler-Bernoulli beam equation that instability understood as a resonance between structural waves coupled to the flow (referred to as flag waves) and free surface waves can occur prior to classical flutter threshold. An analytical analysis will be provided to investigate further the corresponding instability mechanism, and parametric studies will be performed to address instability maps. Finally, the internal tension effect as well as additional results in the more general case of a finite-span flag will also be presented. |
Monday, November 19, 2018 8:52AM - 9:05AM |
F14.00005: 3D wake dynamics and large-amplitude flapping of an inverted elastic flag Pardha Saradhi Gurugubelli Venkata, Rajeev Kumar Jaiman An elastic foil interacting with a uniform flow with its trailing edge clamped, also known as the inverted foil, exhibits a wide range of complex self-induced flapping regimes such as large amplitude flapping (LAF), deformed and flipped flapping. To examine the 3D wake-vortex structures and the LAF response, we present 3D numerical experiments at Reynolds number Re=30,000 by assuming spanwise periodicity. We further investigate the dynamics of a novel inverted foil configuration wherein we introduce a fixed splitter plate at the trailing edge to suppress the vortex shedding from trailing edge and inhibit the interaction between the counter-rotating vortices. Unlike the vortex-induced vibration of an elastically-mounted circular cylinder, we find that the inhibition of the vortex interaction has an insignificant effect on the transverse flapping amplitudes. Finally, we introduce an analogous analytical model for the LAF based on the dynamics of an elastically mounted flat plate undergoing flow-induced pitching oscillations in a uniform stream. |
Monday, November 19, 2018 9:05AM - 9:18AM |
F14.00006: Force drafting of three-dimensional flags in tandem arrangement Fang-Bao Tian The flapping of a flag in a uniform flow is a canonical example of flow-induced vibrations. There have been several experimental and numerical studies on a viscous flow over two two-dimensional flags in tandem arrangement, finding that the downstream flag experiences larger drag than the upstream one if its amplitude is larger. We assume that this is due to the lack of three-dimensional effects. To verify this assumption, an immersed boundary-lattice Boltzmann method is employed to study the force drafting of two three-dimensional flags in tandem arrangement. It is found that for large aspect ratio flags, the three-dimensional force drafting is the same as that of two-dimensional case, while for small aspect ratio flags, the three-dimensional force drafting is the same as two rigid bodies, i.e. the downstream flag experiences smaller drag than the upstream one even its amplitude is larger. |
Monday, November 19, 2018 9:18AM - 9:31AM |
F14.00007: Thrust, drag and wake structure in flapping compliant membrane wings Gali Alon Tzezana, Kenneth Breuer We present results from a theoretical framework developed to characterize the steady and unsteady aeroelastic behavior of compliant membrane wings, relevant to several applications including biological fliers such as bats and colugos, and engineered micro air vehicles (MAVs). The linearized model uses unsteady potential flow coupled to an elastic membrane equation. We use the model to explore the effects of wing compliance, inertia and flapping kinematics on aerodynamic performance. The effects of added mass and fluid damping are quantified using a simple damped oscillator model. We present results showing the optimal conditions for maximum lift and thrust. As the flapping frequency is increased, membranes go through a transition from thrust to drag at a frequency close to the membrane's resonant frequency. This transition is accompanied by a change in the character of the wake from a "reverse von Kármán" to a "von Kármán" vortex wake. The wake transition and the thrust/drag transition do not occur at the same frequency, resulting in some counter-intuitive flows for which thrust is accompanied by a "drag wake", and vice-versa. |
Monday, November 19, 2018 9:31AM - 9:44AM |
F14.00008: Large-amplitude membrane flutter in inviscid flow Christiana Mavroyiakoumou, Silas D Alben We study the dynamics of thin membranes---extensible sheets with negligible bending stiffness---fixed at both ends and aligned with a uniform inviscid background flow. This is a benchmark fluid-structure interaction that has previously been studied mainly in the small-deflection limit, to identify the flutter behavior of membranes. Recent work has also considered applications of thin membranes to shape-morphing airfoils. First, we characterize growth rates and frequencies at small amplitude with respect to mass ratio and membrane pretension. We find general agreement with previous work in the locations of divergence and flutter, but we find an increased range of unstable motions. Our method is able to compute stable large-amplitude motions, but only at sufficiently large stretching modulus. We describe how the membranes' motions and frequencies change in the transition from small- to large- amplitude motions. We also describe transitions from periodic to chaotic dynamics as pretension is decreased and mass ratio is increased. |
Monday, November 19, 2018 9:44AM - 9:57AM |
F14.00009: Dynamics of flexible plates and induced flow under Heaviside acceleration heaving Liu Hong, Jin-Tae Kim, Yaqing Jin, Leonardo P. Chamorro The dynamics of flexible plates under heaving characterized by top-hat acceleration patterns Π(t) and induced flow were experimentally inspected for various Cauchy numbers Ca and fractions of the time under acceleration τ_{a} with respect to the period of oscillations T. Simultaneous measurements of the plate motion along their span and the surrounding flow were obtained with particle tracking velocimetry (PTV) and particle image velocimetry (PIV). Results show the modulation of Ca and τ_{a} on the plate dynamics and, in particular, the induced flow. A simple derived formulation based on the damped harmonic oscillator model effectively predicts the velocity difference between the bottom and top tips of the plates. In general, the plate dynamics and flow exhibited three distinctive patterns characterized by flapping-like motions, intermediate state, and translation-like motions. The occurrence of such patterns depended on the relative instant at the reverse direction within the forced Π(t)-heaving; two of them depending on the sign of u and the other when Δu-> 0, i.e., in the limit of pure translation. |
Monday, November 19, 2018 9:57AM - 10:10AM |
F14.00010: On the Coupled Dynamics of Wall-Mounted Flexible Plates in Tandem Zhongyu Mao, Yaqing Jin, Jin-Tae Kim, Hongyi Zhou, Leonardo P. Chamorro The coupled dynamics of two rectangular, flexible plates of h/b (height/width=4) was experimentally explored in tandem arrangements under uniform flows at various Cauchy numbers (Ca) and spacings. Planar particle image velocimetry and particle tracking velocimetry were used to characterize the surrounding flow and dynamics of the structures. Results indicate that the motions of the upstream plate were governed by its natural frequency, whereas the oscillations of the downstream counterpart were highly modulated by the upstream wake. Such effect led to highly correlated motions between the plates with similar oscillation amplitude under relatively small spacing (0.5h), to comparatively larger amplitude of the downstream structure at intermediate spacing (1h), and nearly decoupled interactions with large gap (2h). Despite that the oscillation intensity of the upstream plate increased monotonically with Ca, this was not the case for the downstream plate at intermediate and large gaps; this resulted in a local minimum. A model is derived to explain this phenomenon, which accounts for the influence of wake fluctuation intensity, vortex shedding and large structure deformation. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2023 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
1 Research Road, Ridge, NY 11961-2701
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700