Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session D18: Vortex Dynamics: Flow Induced Vibrations and Interactions |
Hide Abstracts |
Chair: Jasen Dahl, Ocean Engineering Department, University of Rhode Island Room: 206 |
Sunday, November 22, 2015 2:10PM - 2:23PM |
D18.00001: Three-dimensional flow visualization of a flexible cylinder wake subject to VIV Jason M. Dahl, Emma Thomas, Ersegun D. Gedikli The vortex-induced vibration of a low aspect ratio, low mode number, flexible cylinder is investigated in a recirculating flow channel under uniform inflow conditions. The cylinder had an aspect ratio of 40 and mass ratio of 3.76. The motion of the cylinder is tracked visually, using two high-speed cameras and the intersection of a laser sheet with the cylinder surface, capturing the cross-sectional response of cylinder at various locations along the span. Concurrent with the motion capture system, Particle Image Velocimetry is used to capture the velocity field in the wake of the cylinder at the same locations. The periodic nature of vibrations along the span of the cylinder is used to phase average the motion and wake of the cylinder, allowing for a phase averaged 3-D reconstruction of the cylinder wake. The 3-D reconstruction consists of stereoscopic PIV planar wake measurements obtained at 21 equally spaced locations along the span of the cylinder. The wake is investigated at several speeds showing the excitation of the first mode of the cylinder in the cross-flow direction and the transition to the excitation of the second mode of the cylinder in the in-line direction. This technique is shown to capture 3-D variation of vortex-shedding in the wake of the flexible cylinder. [Preview Abstract] |
Sunday, November 22, 2015 2:23PM - 2:36PM |
D18.00002: VIV of a Flexible Cylinder: Three-dimensional Response Reconstruction from Limited Localized Measurement Points Banafsheh Seyed-Aghazadeh, Yahya Modarres-Sadeghi Vortex-induced vibration (VIV) of a low mass ratio flexible cylinder (m*\textless 1), is studied experimentally. The flexible tension-dominated cylinder was held fixed at both ends and was immersed in the uniform incoming flow. Dynamic response of the system was studied in the reduced velocity range of U*$=$ 2.9 -- 14.5 and the Reynolds number range of Re $=$ 315 -- 1580. Continuous response of the cylinder was reconstructed from limited number of measurement points based on modal expansion theorem modified using Modal Assurance Criterion (MAC). This reconstruction technique made it possible to properly reconstruct a continuous response along the length of the cylinder, even when the measurement points were localized in a small region of the cylinder. Mono- and multi-frequency excitation responses as well as transition from low mode numbers to higher ones were studied. Also, flow forces acting on the cylinder were calculated and they showed a consistent relation between the regions where the cylinder was being excited by the flow (CLv\textgreater 0) and the counterclockwise figure-eight trajectories of oscillations in which the phase difference between the inline and crossflow directions were in the range of $\varphi $xy$=$[0 $\pi $]. [Preview Abstract] |
Sunday, November 22, 2015 2:36PM - 2:49PM |
D18.00003: Regimes of flow induced vibration for tandem, tethered cylinders Gary Nave, Mark Stremler In the wake of a bluff body, there are a number of dynamic response regimes that exist for a trailing bluff body depending on spacing, structural restoring forces, and the mass-damping parameter $m^{*} \zeta$. For tandem cylinders with low values of $m^{*} \zeta$, two such regimes of motion are Gap Flow Switching and Wake Induced Vibration. In this study, we consider the dynamics of a single degree-of-freedom rigid cylinder in the wake of another in these regimes for a variety of center-to-center cylinder spacings (3-5 diameters) and Reynolds numbers (4,000-11,000). The system consists of a trailing cylinder constrained to a circular arc around a fixed leading cylinder, which, for small angle displacements, bears a close resemblance to the transversely oscillating cylinders found more commonly in existing literature. From experiments on this system, we compare and contrast the dynamic response within these two regimes. Our results show sustained oscillations in the absence of a structural restoring force in all cases, providing experimental support for the wake stiffness assumption, which is based on the mean lift toward the center line of flow. [Preview Abstract] |
Sunday, November 22, 2015 2:49PM - 3:02PM |
D18.00004: Wake--induced vibrations in Tandem Cylinders Ravi Chaithanya Mysa, Rajeev Kumar Jaiman The upstream cylinder is fixed in the tandem cylinders arrangement. The downstream cylinder is placed at a distance of four diameters from the upstream cylinder in the free stream direction and is mounted on a spring. The dynamic response of the downstream cylinder is studied at Reynolds number of 10,000. The transverse displacement amplitude of the downstream cylinder is larger compared to that of single cylinder in the post-lock-in region. The transverse dynamic response of the downstream cylinder in the post-lock-in region is characterized by a dominant low frequency component compared to shed frequency, which is nearer to the structural natural frequency. The interaction of upstream wake with the downstream cylinder is carefully analyzed to understand the introduction of low frequency component in the transverse load along with the shed frequency. We found that the stagnation point moves in proportional to the velocity of the cylinder and is in-phase with the velocity. The low frequency component in the stagnation point movement on the downstream cylinder is sustained by the interaction of upstream wake. The frequencies in the movement of the stagnation point is reflected in the transverse load resulting in large deformation of the cylinder. [Preview Abstract] |
Sunday, November 22, 2015 3:02PM - 3:15PM |
D18.00005: Revisiting Vortex Induced Vibration scaling in single degree of freedom systems Vahid Azadeh Ranjbar, NIELL ELVIN, Yiannis Andreopoulos VIV scaling illustrates that the oscillation amplitude of a SDOF circular cylinder mounted on the tip of a flexible cantilever beam is directly proportional to the forcing function and inversely proportional to the damping terms. Past studies that have not considered aerodynamic damping, have showed infinite oscillation amplitude for zero Skop-Griffin number which is unrealistic. A configuration containing a force sensor, strain gauges and a high speed camera is set up to measure aerodynamic forces and damping for stationary and oscillating circular cylinders. Results show that circular cylinder oscillation significantly affects the vortex shedding and consequently aerodynamic forces and damping*. Experimental data show that aerodynamic damping is directly proportional to oscillation amplitude but this relationship is non-linear for the aerodynamic force. These experimental data have been used to revisit VIV scaling. Comparison between our experimental data and experimental data of past studies in Griffin plot under the new scaling have showed very good agreement. [Preview Abstract] |
Sunday, November 22, 2015 3:15PM - 3:28PM |
D18.00006: Streamwise Oscillations of Freely Vibrating Circular Cylinder in the Vicinity of a Stationary Wall Rajeev Jaiman, Daniel Tham, Li Zhong, Pardha Gurugubelli We present a numerical study on vortex-induced vibration (VIV) of a freely vibrating two degree-of-freedom circular cylinder in close proximity to a stationary plane wall. Fully implicit combined field scheme based on Petrov-Galerkin formulation has been employed to analyze the nonlinear effects of wall proximity on the vibrational amplitudes and hydrodynamic forces. Two-dimensional simulations are performed as function of decreasing gap to cylinder diameter ratio $e/D\in[0.5,10]$ for reduced velocities $U^*\in[2,10]$ at $Re_D=100$ and $Re_L=2900$, where $Re_D$ and $Re_L$ denote the Reynolds numbers based on the cylinder diameter and the upstream distance, respectively. We investigate the origin of enhanced streamwise oscillation of freely vibrating near-wall cylinder as compared to the isolated cylinder counterpart. For that purpose, detailed analysis of the amplitudes, frequency characteristics and the phase relations has been performed for the isolated and near-wall configurations. Initial and lower branches in the amplitude response are found from the gap ratios of 0.75 to 10, similar in nature to the isolated cylinder laminar VIV. For near-wall cases, phase relation between drag force and streamwise displacement varies from close to $0^{\circ}$ to $180^{\circ}$. Effects of mass-ratio, thickness of wall boundary layer and cylinder depth from the top surface are further investigated. Finally, we introduce new correlations for characterizing peak amplitudes and forces as a function of the gap ratio for a cylinder vibrating in the vicinity of a stationary plane wall. [Preview Abstract] |
Sunday, November 22, 2015 3:28PM - 3:41PM |
D18.00007: Hysteretic memory and end plate effects on the response of a flexible cylinder undergoing Vortex-Induced Vibrations (VIV) Ersegun Deniz Gedikli, Jason M Dahl The response of rigid cylinders undergoing VIV has been observed to be hysteretic with respect to the nominal reduced velocity, as transition of the wake is delayed dependent on whether the flow has been slowed down or sped up. In the present study, a similar behavior is observed for a flexible, tension-dominated cylinder, however the hysteretic behavior is shown to affect the transition between excited modes. The test cylinder has diameter of 6.35 mm, aspect ratio of 40 and mass ratio of 3.76. The dynamic response of the cylinder is measured visually, by tracking 26 dots along the span of the cylinder using two high-speed cameras between the Reynolds number of 1080 and 4660. It is observed that a clear memory effect exists, where the speed at which transition between the first mode and second mode excitation in the cross-flow direction changes dependent on whether the flow is increasing or decreasing in speed. A second series of experiments is conducted to investigate end plate effects on the flexible cylinder. Experiments are conducted with and without an end plate located at the end pivot point on the cylinder. Clear differences are observed between each condition illustrating the strong three-dimensional behavior of vortex shedding behind the flexible cylinder. [Preview Abstract] |
Sunday, November 22, 2015 3:41PM - 3:54PM |
D18.00008: Flow-induced oscillations of a prism with triangular cross-section placed in water Daniel Carlson, Banafsheh Seyed-Aghazadeh, Yahya Modarres-Sadeghi Flow-induced oscillations of a prism with a triangular cross-section was studied experimentally. The cylinder had one-degree-of-freedom to oscillate in the crossflow direction. The response of the cylinder in terms of the amplitudes of oscillations as well as the flow forces were studied at varying angles of attack in the range of $\alpha =$0$^{\circ}$ -60$^{\circ}$ and a reduced velocity range of U*$=$4-22. Depending on the angle of attack and the reduced velocity, the cylinder experienced either VIV or galloping. For small angles of attack of $\alpha $\textless 30$^{\circ}$, the cylinder did not oscillate while for larger angles of $\alpha =$30$^{\circ}$ and 35$^{\circ}$, the cylinder underwent VIV in a range of reduced velocities (U*$=$7-14.5) and galloping at higher reduced velocities (U*$=$19.5-22). The conducted dye flow visualization as well as the measured flow forces confirmed the existence of lock-in as well as galloping-type response. For larger angles of attack of $\alpha $\textgreater 35$^{\circ}$, the amplitude of oscillations increased monotonically with increasing reduced velocity and the cylinder underwent galloping. Several different vortex shedding patterns were observed in the wake of the cylinder at different angles of attack and flow velocities. New, high-frequency shedding patterns with their corresponding high harmonic shedding frequencies in the flow force FFTs were observed in the regions where galloping occurred. [Preview Abstract] |
Sunday, November 22, 2015 3:54PM - 4:07PM |
D18.00009: Two-Dimensional Vortex-Induced Vibration of a Curved Cylinder Lauren Bouchard, Daniel Carlson, Banafsheh Seyed-Aghazadeh, Yahya Modarres-Sadeghi We study vortex-induced vibration of a flexibly-mounted rigid curved cylinder placed in flow either in the concave or the convex orientation. The ratio of the structural natural frequencies in the inline and crossflow directions was varied from 1 to 2 in steps of 0.2. Counterclockwise figure eights were observed in the convex orientation when the structural natural frequency ratio was 2. For all the other frequency ratios tested (1, 1.2, 1.4, 1.6 and 1.8) the motion was mainly in the crossflow direction, with very small inline amplitudes. This was also the case for the cylinder in the concave orientation with a frequency ratio of 2. Overall the crossflow amplitudes were larger for the 2D case compared with the crossflow amplitudes of the same cylinder with only one degree of freedom in the crossflow direction. [Preview Abstract] |
Sunday, November 22, 2015 4:07PM - 4:20PM |
D18.00010: Two-dimensional wakes of oscillating and tandem cylinders at low Reynolds number Wenchao Yang, Mark Stremler Transverse flow past an oscillating bluff body or multiple stationary bodies can produce wakes with complicated spatio-temporal structure. Previous work by others has characterized the wake structure as a function of system parameters. These are typically 2D characterizations, despite the fact that instabilities often cause such wakes to become strongly 3D. We use a flowing soap film system to investigate the connections and differences between (quasi) 2D wakes and 3D wakes generated behind oscillating and tandem cylinders. Wake structure is identified through flow visualization. Inspired by the work of Williamson and collaborators, we investigate the wake structure behind a circular cylinder forced to oscillate transverse to the flow. We map the boundaries of the different wake modes with variations in the amplitude and frequency of oscillation, and we discuss how our quasi-2D results compare with 3D results from the literature. We also consider the wake interaction of two stationary cylinders arranged in tandem. Existing literature disagrees on the critical cylinder spacing that gives changes in the wake mode. We examine this point and discuss the connections and distinctions between our quasi-2D experiments, 2D simulations, and results from the literature. [Preview Abstract] |
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. |
© 2024 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
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700