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 A10: Vortex Dynamics and Vortex Flow: General I |
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Chair: Yahya Modarres-Sadeghi, U. Mass Amhearst Room: 3A |
Saturday, November 23, 2019 3:00PM - 3:13PM |
A10.00001: On the Morison equation and heave plate hydrodynamics Curtis Rusch, Benjamin Maurer, Brian Polagye Ocean wave energy converters often use a submerged reaction body, such as a heave plate, to generate electricity from wave motion. Analysis of heave plate hydrodynamics typically utilizes the Morison equation to estimate the contributions of drag and inertia to hydrodynamic force, neglecting further components, such as the vortex force discussed extensively by Sarpkaya. We perform laboratory experiments to evaluate the representativeness of a Morison decomposition over a range of operational and survival states, representing Keulegan-Carpenter (KC) numbers of 0.5 to 4. Driving a hexagonal conic heave plate in regular sinusoidal motion with 17 combinations of period and amplitude, we measure force at the plate and visualize the surrounding flow. Using the Morison equation, we calculate both constant coefficients of drag and added mass and phase-dependent variable coefficients. We find that constant coefficients adequately describe hydrodynamic force at low KC number, but this accuracy decreases with increasing KC number. Variable coefficients accurately reconstruct hydrodynamic forces over the full range of KC numbers investigated. We discuss this discrepancy in the context of the vortex term using dye visualization, and discuss implications for wave energy converter design. [Preview Abstract] |
Saturday, November 23, 2019 3:13PM - 3:26PM |
A10.00002: Vortex-Induced Vibration and Galloping of a Flexible Square Prism. Ronald Colmon, Yahya Modarres-Sadeghi We have studied flow-induced oscillations of a tension-dominated flexible beam with a square cross-section placed perpendicular to the incoming flow. The prism with an aspect ratio of 32 was fixed at its both ends and placed in the test-section of a recirculating water tunnel. The Reynolds number was varied from 400 to 2400. Tracker points were evenly spread along the length of the prism, on two perpendicular sides, in order to measure the prism's displacements in the crossflow (CF) and inline (IL) directions. Displacements of these points were tracked using two synchronized high speed cameras. It was found that at low reduced velocities the first and then the second structural modes were excited in the CF direction, together with the second and the fourth modes in the inline direction, resulting in vortex-induced vibration with ``figure 8'' trajectories. At higher reduced velocities, the amplitude of oscillations increased dramatically, and galloping-type oscillations were observed. [Preview Abstract] |
Saturday, November 23, 2019 3:26PM - 3:39PM |
A10.00003: The formation process of leading and secondary vortices Diego Francescangeli, Karen Mulleners Vortex formation is a limiting process. When a plate is accelerated from rest or fluid is impulsively ejected from a piston-cylinder apparatus, a primary or leading vortex grows in size and strength up to a limit when it pinches-off. Beyond this point, secondary vortices akin to a Kelvin-Helmholtz instability are generated. These secondary vortices are similar to each other but smaller in size and lower in strength than the leading vortex. The motivation to understanding the difference between the leading and secondary vortices, leads us to study the formation process of vortices around a moving rectangular plate in a quiescent fluid. Eulerian and Lagrangian methods are used to track vortices and determine their circulation, vorticity distribution, and size from experimental velocity field data. The experimental data is further compared with different theoretical vortex models to elucidate the differences between the formation process of the leading and the secondary vortices. [Preview Abstract] |
Saturday, November 23, 2019 3:39PM - 3:52PM |
A10.00004: Dynamics and flow structures in the vortex-induced vibration of a curved flexible cylinder Banafsheh Seyed-Aghazadeh, Bridget Benner, Xhino Gjokollari, Yahya Modarres-Sadeghi Vortex-induced vibration of a curved flexible circular cylinder placed in the test section of a re-circulating water tunnel and fixed at both ends was studied, experimentally. Both the concave and the convex orientations (with respect to the oncoming flow direction) were considered. The cylinder was tension-dominated by its own weight with an aspect ratio of 86 and a low-mass ratio of a 3.7. High-speed imaging technique was employed to record the oscillations of the cylinder in the crossflow direction for a reduced velocity range of $U$* $=$ 4.8- 42.3, corresponding to a Reynolds number range of \textit{Re }$=$ 370-2400. Mono- and multi-frequency responses as well as transition from low mode numbers to high mode numbers are observed. Regardless of the type of curvature, both odd and even mode shapes are excited in the crossflow directions. However, the response of the system, in terms of the excited modes, amplitudes and frequencies of oscillations, is observed to be sensitive to the direction of curvature (concave vs. convex), in particular at higher reduced velocities where mode transition happens. Hydrogen bubble image velocimetry flow visualization was conducted at multiple points along the length of the curved cylinder. Intermittency in the vortex shedding patterns in the wake of the cylinder and alternating wake along the cylinder are observed. The observed altering wake corresponds to the multi-modal excitation and dominant mode transition along the length of the cylinder. [Preview Abstract] |
Saturday, November 23, 2019 3:52PM - 4:05PM |
A10.00005: Decay of vortex rings in spheroidal confined domains Milad Samaee, Arvind Santhanakrishnan Recent studies studied the decay of vortex rings in radially confined domains; however, the vortex ring decay process in spheroidal confinement (axial and longitudinal confinement) remains unclear. This type of confinement is observed in the vortex rings formed during filling of the human cardiac left ventricle. We hypothesized that the rate of circulation decay increases in more axially confined domains. A piston-cylinder setup was used to generate vortex rings for this study. 2D time-resolved PIV was used to quantify the flow fields within three different aspect ratios of spheroidal silicone models (0.8, 1, and 1.25) under different filling duration, Reynolds number, and deceleration time. The formation number and peak circulation remained unaffected regardless of model shape. However, for the cases with the same filling duration, the vortex ring pinched-off earlier by shortening the acceleration time. We observed a higher rate of decay for the model with a lower aspect ratio (more axially confined). [Preview Abstract] |
Saturday, November 23, 2019 4:05PM - 4:18PM |
A10.00006: ABSTRACT WITHDRAWN |
Saturday, November 23, 2019 4:18PM - 4:31PM |
A10.00007: ABSTRACT WITHDRAWN |
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