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 G27: Biofluids: Propulsion: Interactions, Wakes and Jets |
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Chair: Leah Mendelson, MIT Room: 308 |
Monday, November 23, 2015 8:00AM - 8:13AM |
G27.00001: Application of a discretized vortex impulse framework to fish maneuvering Leah Mendelson, Alexandra Techet In studies of biological propulsion, metrics for quantitative analysis of the vortex wake, including circulation, impulse, and their time derivatives, are a valuable indicator of performance. To better utilize volumetric PIV data in this type of analysis, a discretized method of deriving vortex impulse relying only on velocity data is developed. The impulse formulation is based on the geometry and distribution of circulation along the vortex core line, which can be detected using critical points in the velocity field. This analysis method is then applied to time-resolved velocity data of a turning giant danio (\textit{Devario aequipinnatus}) and a jumping archer fish (\textit{Toxotes microlepis}) obtained using Synthetic Aperture PIV (SAPIV). In the case of the danio, the vortex force vector derived from the impulse derivative shows good agreement with the kinematics of the fish tail during the turning maneuver. With the archer fish, the model is used to explore the relationship between the number of tail beats prior to the jump and the jump height. [Preview Abstract] |
Monday, November 23, 2015 8:13AM - 8:26AM |
G27.00002: Experimental study of Strouhal number effects on the wake produced by a trapezoidal pitching panel Justin King, Melissa Green Stereoscopic particle image velocimetry (PIV) was used to characterize the highly three-dimensional wake produced by a rigid, bio-inspired trapezoidal pitching panel. Previous work has demonstrated that one of the dominant parameters governing the wake structure of a pitching panel is the Strouhal number, and detailed analysis in terms of Strouhal number is the focus of the current work. Experiments were conducted over a range of Strouhal numbers from 0.17 to 0.56, and PIV data were collected in 55 planes across the spanwise extent of the wake. Examination of the spanwise vorticities and spanwise velocities found in the wake allow for an investigation into wake breakdown and spanwise wake compression behaviors. The results showed that increases in Strouhal number were associated with the movement of the wake breakdown location upstream and greater spanwise compression of the wake. [Preview Abstract] |
Monday, November 23, 2015 8:26AM - 8:39AM |
G27.00003: ABSTRACT WITHDRAWN |
Monday, November 23, 2015 8:39AM - 8:52AM |
G27.00004: Synchronized Swimming of Two Fish Petros Koumoutsakos, Guido Novati, Gabriele Abbati, Babak Hejazialhosseini, Wim van Rees We present simulations of two, self-propelled, fish-like swimmers that perform synchronized moves in a two-dimensional, viscous fluid. The swimmers learn to coordinate by receiving a reward for their synchronized actions. We analyze the swimming patterns emerging for different rewards in terms of their hydrodynamic efficiency and artistic impression. [Preview Abstract] |
Monday, November 23, 2015 8:52AM - 9:05AM |
G27.00005: A dynamical system for interacting flapping swimmers Anand Oza, Sophie Ramananarivo, Leif Ristroph, Michael Shelley We present the results of a theoretical investigation into the dynamics of interacting flapping swimmers. Our study is motivated by the recent experiments of Becker et al.,\footnote{Becker, A., Masoud, H., Newbolt, J., Shelley, M. \& Ristroph, L. \lq\lq Hydrodynamic schooling of flapping swimmers\rq\rq\, (submitted).} who studied a one-dimensional array of self-propelled flapping wings that swim within each other's wakes in a water tank. They discovered that the system adopts certain \lq\lq schooling modes\rq\rq\, characterized by specific spatial phase relationships between swimmers. To rationalize these phenomena, we develop a discrete dynamical system in which the swimmers are modeled as heaving airfoils that shed point vortices during each flapping cycle. We then apply our model to recent experiments in the Applied Math Lab, in which two tandem flapping airfoils are free to choose both their speed and relative positions. We expect that our model may be used to understand how schooling behavior is influenced by hydrodynamics in more general contexts. [Preview Abstract] |
Monday, November 23, 2015 9:05AM - 9:18AM |
G27.00006: Vortex interaction between two tandem flexible propulsors Sung Goon Park, Hyung Jin Sung Schooling behaviors of flying and swimming animals are widespread phenomena in nature. Inspired by schooling behaviors of swimming jellyfish, self-propelling flexible bodies with a paddling-based locomotion were modeled in a tandem configuration. The interactions between surrounding fluids and propulsors were considered by using the immersed boundary method. The hydrodynamic patterns generated by the interactions between tandem flexible propulsors were analyzed in the presen study. As a result of the flow-mediated interactions between them, stable configurations were formed spontaneously in which the gap distance between propulsors increased and decreased during the contraction and relaxation phases of the upstream propulsor. The stable configuration was not affected by the initial gap distance but influenced by the phase difference in the flapping frequency between them. Both tandem propulsors benefited from the tandem configuration in terms of the locomotion as compared with an isolated propulsor. [Preview Abstract] |
Monday, November 23, 2015 9:18AM - 9:31AM |
G27.00007: Locomotion gaits of a rotating cylinder pair Wim M. van Rees, Guido Novati, Petros Koumoutsakos, L Mahadevan Using 2D numerical simulations of the Navier-Stokes equations, we demonstrate that a simple pair of rotating cylinders can display a range of locomotion patterns of biological and engineering interest. Steadily counter-rotating the cylinders causes the pair to move akin to a vortex dipole for low rotation rates, but as the rotational velocity is increased the direction of motion reverses. Unsteady rotations lead to different locomotion gaits that resemble jellyfish (for in-phase rotations) and undulating swimmers (for out-of-phase rotations). The small number of parameters for this simple system allows us to systematically map the phase space of these gaits, and allows us to understand the underlying physical mechanisms using a minimal model with implications for biological locomotion and engineered analogs. [Preview Abstract] |
Monday, November 23, 2015 9:31AM - 9:44AM |
G27.00008: Bio-inspired Propulsion with Functionally Graded Materials William Schleicher, Daniel Floryan, Tyler Van Buren, Alexander Smits, Keith Moored From an engineering perspective, biological swimmers are a composite material system with varying material properties across their propulsors. These material properties govern how the swimmer's structure interacts with its surrounding fluid. A two dimensional boundary element fluid solver is strongly coupled to a direct, implicit, geometrically non-linear structure solver to study the effects of functionally graded materials. A zeroth order functionally graded material approximation is used, where a rigid material abruptly meets a flexible material. Thrust, input power, and propulsive efficiency are studied as functions of non-dimensional frequency, reduced frequency, Strouhal number, flexion ratio, and effective stiffness. The numerical results are compared to experimental results for zero attack angle cases, building confidence in the numerical model. The results are further compared to structurally rigid materials. [Preview Abstract] |
Monday, November 23, 2015 9:44AM - 9:57AM |
G27.00009: Jet vectoring through nozzle asymmetry Chris Roh, Alexandros Rosakis, Morteza Gharib Previously, we explored the functionality of a tri-leaflet anal valve of a dragonfly larva. We saw that the dragonfly larva is capable of controlling the three leaflets independently to asymmetrically open the nozzle. Such control resulted in vectoring of the jet in various directions. To further understand the effect of asymmetric nozzle orifice, we tested jet flow through circular asymmetric nozzles. We report the relationship between nozzle asymmetry and redirecting of the jet at various Reynolds numbers. [Preview Abstract] |
Monday, November 23, 2015 9:57AM - 10:10AM |
G27.00010: Multi-jet propulsion organized by clonal development in a colonial siphonophore John Costello, Sean Colin, Brad Gemmell, John Dabiri, Kelly Sutherland Physonect siphonophores are colonial cnidarians that are pervasive predators in many neritic and oceanic ecosystems. Physonects employ multiple, clonal medusan individuals, termed nectophores, to propel an aggregate colony. Here we show that developmental differences between clonal nectophores of the physonect \textit{Nanomia bijuga} produce a division of labor in thrust and torque production that controls direction and magnitude of whole colony swimming. Although smaller and less powerful, the position of young nectophores near the apex of the nectosome allows them to dominate torque production for turning whereas older, larger and more powerful individuals near the base of the nectosome contribute predominantly to forward thrust production. The patterns we describe offer insight into the biomechanical success of an ecologically important and widespread colonial animal group, but more broadly, provide basic physical understanding of a natural solution to multi-engine organization that may contribute to the expanding field of underwater distributed propulsion vehicle design. [Preview Abstract] |
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