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 P14: Vortex Induced Vibration |
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Chair: David Olson, Michigan State University Room: 307/308 |
Monday, November 25, 2019 5:16PM - 5:29PM |
P14.00001: A passive amplification of VIV through a semi-hollow cylinder for Reynolds number 200 Sungmin Ryu, Seungmin Kang Since the demonstration that the kinetic energy generated by vortex-induced vibrations (VIVs) can be converted into electricity, the amplification of VIV has been of significant interest. For this practical relevance, we present a passive method to amplify VIVs of a circular cylinder for Reynolds number 200. We employ an empty space inside a solid circular cylinder and place an orifice on the stagnation point to embody a concept of passive control, considering a potential combination with existing passive devices. We quantified the performance of the semi-hollow model via two-dimensional simulations for a range of reduced velocity 3$\le U_{red}\le $8, and these are compared to solid cylinder counterparts. We show that significant elevations of the transverse force and the dynamic response are achieved by the semi-hollow body under the synchronization condition as well as otherwise ones. In addition, the transverse net force acting on the inner surface of the semi-hollow cylinder is shown to be developed in time as a consequence of internal flow circulations, and this is asserted as a key role for the amplification. [Preview Abstract] |
Monday, November 25, 2019 5:29PM - 5:42PM |
P14.00002: Transverse vortex-induced vibrations of a prolate spheroid Alvaro Sanchez Ruiz, Remi Bourguet, Guillaume Martinat A prolate spheroid of aspect ratio 6:1 can be regarded as a simplified model of the hull of an aeronautical or underwater vehicle. From a fundamental perspective, it represents an intermediate geometry between a sphere and an infinite circular cylinder, which have often served as paradigms to study bluff body wakes and flow-induced vibrations. When a rigidly mounted, prolate spheroid is placed in a cross-current, i.e. a flow normal to its long axis, previous studies have shown that its unsteady wake is characterized by the formation of large-scale hairpin vortices, which result in fluctuations of fluid forces. The case where the spheroid is elastically mounted and the possible occurrence of flow-induced responses of the body remain to be explored. This is the object of the present work where the spheroid is free to vibrate in the transverse direction. On the basis of direct numerical simulations, the behavior of the coupled flow-structure system is examined, at Reynolds number 100, over a wide range of values of the oscillator natural frequency. Focus is placed on the emergence of vortex-induced vibrations and on the associated alteration of the flow dynamics, compared to the stationary body wake. [Preview Abstract] |
Monday, November 25, 2019 5:42PM - 5:55PM |
P14.00003: Combined vortex-induced vibration of a rigid cylinder and a detached flexible splitter-plate Charu Mittal, Atul Sharma A 2D numerical study on vortex induced vibration (VIV) of a rigid cylinder and a flexible splitter-plate is presented, using our immersed interface method based in-house code. In the present work, the effect of cylinder-plate spacing S* ($=$0.51-3) and the reduced velocity U* ($=$1-12.5), on the periodic flow-structures and the energy harvesting potential, is studied at constant Reynolds number Re$=$100, cylinder mass ratio M*$=$1, and damping coefficient $\zeta =$0.005. The transverse vibrations of the cylinder are significantly enhanced at larger U* for smaller S*. The enhanced oscillations at larger U* resulted in a novel vortex shedding pattern, comprising of pairs of cylinder and plate vortices, as compared to 2S pattern for the vibration of only rigid cylinder at smaller Re. The vortex pattern at low and intermediate U* continue to remain the same as that obtained without the plate; 2S and C(2S) respectively. The interaction of the plate and the cylinder vortices leads to plate tip-displacement enhancement at smaller S* and intermediate U*. The overall cylinder-plate response indicates maximum energy harvesting potential at high U* and low S*. The present work is the first study on the combined VIV and presents a promising system for energy harvesting. [Preview Abstract] |
Monday, November 25, 2019 5:55PM - 6:08PM |
P14.00004: ABSTRACT WITHDRAWN |
Monday, November 25, 2019 6:08PM - 6:21PM |
P14.00005: Wind-induced response of 3 coupled flexible cylinders. Jannette Frandsen, Teis Schnipper, Svend Ole Hansen Wind-induced vibrations of 3 flexible circular cylinders have been measured in low turbulence flow conditions. The rigid cylinders are closely spaced and physically coupled giving rise to wake interactions. They are arranged in an equilateral triangle. The tests have been conducted on a section model elastically suspended for different angles-of-attack and spacing ratios. All results are based on self-excited structural responses for test cases of undamped and damped structures in the subcritical Reynolds no. range. Cross-flow Vortex/Wake-Induced Vibrations (VIV/WIV) in pure heave motion were identified. These were typically double responses resulting in a wide Strouhal no. range. Oscillation hysteresis contributed to the lowest onset. A special case related to torsion was also identified. The stability of the structure depends on the mass-damping parameter, the Scruton no. The Galloping-Induced Vibrations (GIV) are special cases identified because VIV and GIV couple when the Scruton no. is relatively low. When this coupling occurs, large vibrations develop. Thus, structural design, to include dampers, should assure that the Scruton no. is above a certain minimum value which has been identified to be substantially higher than the ones related to pure VIV/WIV cases. [Preview Abstract] |
Monday, November 25, 2019 6:21PM - 6:34PM |
P14.00006: Experimental investigation of the boundary layer behavior on rectangular cylinders with surface topology Kian Kalan, Mark Feero, Ahmed Naguib, Manoochehr Koochesfahani This work is motivated by possible galloping instability of suspension lines of precision airdrop systems. This aero-elastic instability may lead to self-sustained oscillation due to the unsteadiness in the aerodynamic forces, induced by variation in the instantaneous angle of attack as the cable oscillates normal to the mean flow direction. In order to have better insight into the underlying flow physics, one-component molecular tagging velocimetry has been employed in this study to measure the boundary layer development on cylinders with canonical geometry representing the suspension line cross-section. Specifically, those cylinders have rectangular cross-section with thickness d, side ratio and corner radius of c/d $=$ 2.5 and r/d $=$ 0.5, respectively, and surface topology. Results will be presented for Reynolds numbers of Re$_{\mathrm{d\thinspace }}=$ 1100 and 2500, with focus on cross-stream profiles of the mean and the fluctuating streamwise velocity component for a range of angles-of-attack. Data will also be presented for baseline smooth-surface cylinders in order to investigate the effect of surface topology. [Preview Abstract] |
Monday, November 25, 2019 6:34PM - 6:47PM |
P14.00007: Discovering time-varying aerodynamics of a prototype bridge during vortex-induced vibrations Shanwu Li, Eurika Kaiser, Shujin Laima, Hui Li, Steven L. Brunton, J. Nathan Kutz Vortex-induced vibrations (VIVs) of a long-span bridge are measured based on the structural health monitoring (SHM) system. The significantly nonstationary wind flow in the field results in intrinsically time-varying aerodynamics, which is difficult to describe by the laboratory model (Ehsan and Scanlan, 1990) with the stationary (or steady) flow assumption. We thus propose a slight variant of \textit{sparse identification of nonlinear dynamics} (SINDy) (Brunton et al., 2016) to discover a parsimonious, time-dependent ordinary differential equation of the vibration amplitude that captures the wind-bridge interactions from the field measurements. The library of candidate nonlinear functions is constructed based on the laboratory model. A moving time window is introduced to apply a typical SINDy regression at each time instant during the VIV event. A time series of sparse coefficient vectors of the candidate functions are obtained to reveal the time-varying aerodynamics. It is found that the level of self-excited effects is significantly varying with the temporal wind flow and bridge motion state. Further, cluster analysis of the obtained coefficient vectors for all VIV events has identified dynamical regimes distinguished by level of self-excited effects. [Preview Abstract] |
Monday, November 25, 2019 6:47PM - 7:00PM |
P14.00008: Vortex-Induced Vibrations of a rigid cylinder with forced axial rotations Francisco Huera-Huarte The vortex-induced vibrations (VIV) of a rigid cylinder forced to oscillate around its axis with different amplitudes and frequencies has been studied. A rig allows the cylinder to vibrate with one degree-of-freedom cross-flow, and at the same time rotations can be applied. We will show the effects of the ratio of the frequency of rotational oscillations to that of the VIV, on the dynamics of the system. A very wide parameter space has been covered, including cases in which the forced frequency is controlled in closed loop using the frequency of VIV oscillations. The model hangs from an air bearing rig so the full one degree-of-freedom dynamic response of the system can be measured in detail when subject to different uniform currents imposed in a recirculating water tunnel, while the rotational oscillations are imposed. The latter are also measured using non-intrusive techniques. The flow dynamics around the system have been measured using planar Particle Image Velocimetry for specific cases. Results will show very complex dynamics and the effect of the amplitude, frequency and phase of rotation imposed to the cylinder, which is compared to the classical well-known VIV response of low mass-damping systems. [Preview Abstract] |
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