Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session R04: Locomotion: Fish Swimming |
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Chair: Catherine Wilson, Cardiff University Room: Ballroom D |
Monday, November 25, 2024 1:50PM - 2:03PM |
R04.00001: ABSTRACT WITHDRAWN
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Monday, November 25, 2024 2:03PM - 2:16PM |
R04.00002: Hydrodynamics of Thunniform Swimming: Self-propelled Large-Eddy Simulations Roopesh Kishan Mallepaddi, Vadim V Pavlov, Barbara A Block, Iman Borazjani The effects of Reynolds Number on a self-propelled virtual tuna are investigated using Large-Eddy Simulation Curvilinear Immersed Boundary (LES-CURVIB) method. The kinematics of the swimmer are prescribed based on experimental observations provided by the Hopkins Marine Station at Stanford University. Simulations are performed at the biologically relevant Reynolds Number (Re) of 1.1 million and artificial lower ones of 4000 and 40000. Wall-resolved LES has been performed for Re = 40000 and log-law wall model has been used for Re = 1.1 million. The simulations show that the Froude efficiency of the swimmer is much higher at the biological Re compared to the intermediate and lower Re. A leading-edge vortex has been observed on the tail which increases the thrust generation by generating a reduced pressure region at the leading edge. |
Monday, November 25, 2024 2:16PM - 2:29PM |
R04.00003: Rainbow Trout Responses to Twin Vertical Axis Turbine Hydrodynamics in an Experimental Flume Catherine Wilson, Guglielmo Sonnino Sorisio, Stephanie Muller, Jo Cable, Pablo Ouro Increased energy security and access in remote communities is a target of the UN’s Sustainable Development Goals. To achieve this renewable energy sources with minimal environmental impact are the preferred solution. Hydropower dams a common renewable energy yet they have a large impact on river connectivity causing mortality in migratory fish and extensive sediment trapping upstream of dams. Vertical Axis Turbines (VAT) are a type of hydrokinetic turbine that allow energy extraction from flowing rivers without impounding water, however their environmental impact is unknown. We performed hydrodynamic analysis on three configurations of single and paired VATs in an experimental flume and then allowed groups of three rainbow trout (Oncorhynchus mykiss) to interact with the turbines and tracked their behaviour. A single VAT produced a wake characterised by high vorticity bounding either side of the wake and increased turbulence. When paired with another VAT, the interaction between turbine wakes led to a merged wake that evolved differently downstream depending on their relative rotation direction due to interaction from the wakes of both turbines. The fish responded to the turbines with general avoidance and blade strikes were extremely rare. Importantly, the turbines did not impede passage upstream of the turbines. When shoaling the fish were bolder, spent more time in the near wake and bow wake compared to single fish, and they also spent less time resting. |
Monday, November 25, 2024 2:29PM - 2:42PM |
R04.00004: Persistent homology of a bioinspired model fin vortex wake Alemni Yiran, Marko Budisic, Melissa A Green Topology is a branch of mathematics concerned with the properties of a geometric object that are preserved under continuous deformations, i.e. without closing/opening holes, tearing, gluing, or passing through itself. We interpret the vorticity field of a bio-inspired pitching panel wake as a two dimensional set that has structure, or topology, that we wish to uncover. Specifically, we examine the efficacy of persistent homology (PH), a topological data analysis (TDA) technique used to decipher complex data by detecting and tracking topological features, within the field of fluid dynamics— a relatively new endeavor. Results show that using TDA to analyze these flow field sets identifies vortex cores and boundaries as persistent features by examining the H0 and H1 homology groups. Furthermore, metrics such as a bottleneck or Wasserstein distance provide a path for quantifying the significance of vortex shedding and the corresponding change in topology. This work investigates how the changes in flow field topology, as identified with PH, correspond to measured thrust production, time-averaged efficiency, and planform geometry for a range of bioinspired pitching panels. |
Monday, November 25, 2024 2:42PM - 2:55PM |
R04.00005: Asymmetries in passive propulsion of a flexible foil under water waves Ming Li, Sung Goon Park, Lian Shen Fish swimming close to water wave surfaces can extract wave energy to produce thrust and save their energy expenditure. To understand this passive propulsion mechanism, we investigated the unsteady motions of a two-dimensional flexible foil in an incident wave. The fluid-structure interaction problem was simulated using a diffused immersed boundary (IB) method, together with a coupled level set and volume-of-fluid (CLSVOF) method to capture the wave surfaces. After reaching a periodic steady state, the passive propulsion performances are asymmetrical in up- and downstroke, including the thrust force and wave energy extraction. Detail kinematics studies show that the passive flapping motion is asymmetric in the upstroke and downstroke, with an increased trailing edge amplitude and a higher vertical speed during the upstroke when the foil approaches the wave surface. These asymmetries are attributed to the passing-over leading-edge vortex (PO-LEV), where a vortex pair, formed at the leading edge of the downside of the foil at the beginning of the upstroke, circumnavigates or passes over the leading edge and rotates to the upside of the foil, and continues to shed into the wake during the rest of the upstroke. The potential impact of the asymmetries on the performance of the passive propulsion will also be investigated. |
Monday, November 25, 2024 2:55PM - 3:08PM |
R04.00006: Morphologically complex biological armor acts as drag reducing agents in benthic fishes Megan Vandenberg, Olivia Hawkins, Adam Summers, Cassandra Donatelli Biological armor is a morphologically diverse feature found across vertebrate taxa from armadillos to crocodiles to several groups of bony fishes. While armor is typically considered defensive, it is a multifunctional trait with many plausible alternative functions. In fishes, armor can act as a shield against abiotic and biotic assaults, be a signal of a quality mate, provide storage for minerals, and act as a system to alter flow around the organism. Here, we explore the hydrodynamic function of armor in twenty species of poacher fishes (Agonidae) by visualizing flow to assess hydrodynamic impacts of different shaped plates. We used micro-computed tomography scans to compare the rugosity across species and geometric morphometrics to capture morphological variation. We then used Digital Particle Image Velocimetry along with 3D printed models of the whole body and scaled up rows of plates to assess overall hydrodynamics as well as the effect of small surface features. Our morphometric analysis revealed that much of the variation in armor morphology is driven by plate shape, spine size and spine prominence. We show that spinier armor reduces drag by generating vortices that keep the boundary layer attached further along the length of the fish, decreasing drag and allowing poachers to expend less energy to stay in place on the benthos. |
Monday, November 25, 2024 3:08PM - 3:21PM |
R04.00007: Modal Dynamics of Plunging Tapered Hydrofoils Brysen Mitchell, Mark Jankauski, Sarah E Morris Many aquatic animals and flying insects rely on flapping appendages for locomotion. The flexibility inherent in these appendages, seen in both fish fins and insect wings, has been correlated with increased efficiency and thrust. The flexural rigidity within these structures is commonly nonuniform and varies along the chord, with the leading edge being stiffer than the trailing edge. This variation in stiffness significantly influences the deformation behavior of the wing or fin, resulting in the propagation of traveling waves along the structure, which is linked to the performance of these animals. This study aims to further understand the relationships between the traveling wave dynamics of flexible foils with taper along the chord (varied geometrical stiffness) as a response to imposed motion profiles, and the output thrust. In this work, rectangular foils undergo a sinusoidal heaving motion with varied amplitude and frequency. Modal analysis is performed using a scanning laser vibrometer to measure resonant frequencies and 2D mode shapes of the foils in quiescent water as the imposed amplitude is varied. The complex indicator function is used to quantify the deformation behavior of the foils as standing or traveling waves at each amplitude. Particle image velocimetry is used to quantify the thrust from the wake of the foils. |
Monday, November 25, 2024 3:21PM - 3:34PM |
R04.00008: Effects Fin Geometry and Fin Ray Stiffness on the Performance of Bio-inspired Flapping Propulsion Alec Menzer, Menglong Lei, Joseph J Zhu, Hilary Bart-Smith, Haibo Dong Many examples of flexible surfaces can be found in natural propulsors. Here, we take inspiration from the spiny fin rays exhibited by real tuna fins to alter the flexibility of fin structures on the bio-inspired swimming robot platform, tunabot. This work utilizes a computational model of the tunabot featuring reconstructed body, dorsal, anal, and caudal fin surfaces. Fin geometry, stiffness, and fin ray patterns of the median fins (dorsal and anal fins) are altered to understand the effect on vortex interactions between the median fins and caudal fin, and hydrodynamic force and moment production on the surfaces. Flow information is solved using an in-house developed immersed boundary method based incompressible Navier-Stokes flow solver. Deformations of the fins due to the hydrodynamic forces are computed using Vega FEM. Iterative convergence of the fluid and structure solvers within each time step yields two-way coupled fluid-structure interaction (FSI) simulations. Results in this talk highlight the role of ray stiffness and geometry in altering the hydrodynamic forces of the propulsive caudal fin and undulating body. Furthermore, we will discuss the ability of these fin properties to enhance near-body flow structures. Findings of this research will help inform the design of bio-inspired fins for efficient underwater robots. |
Monday, November 25, 2024 3:34PM - 3:47PM |
R04.00009: Abstract Withdrawn |
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