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 G03: Focus Session: Fish Swimming Kinematics and Hydrodynamics I |
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Chair: Catherine A.M.E. Wilson Room: 201 |
Sunday, November 24, 2019 3:48PM - 4:01PM |
G03.00001: Fish out of water: hydrodynamics from swimming to jumping Invited Speaker: Alexandra H. Techet Aquatic jumping is widely revered with awe by humans, as evidenced in the popularity of the Discovery Channels "Shark Week" episodes on jumping sharks. Jumping by any organism requires high bursts of power and muscular coordination. Aquatic jumpers in particular must produce thrust in manners compatible with the transition from one fluid media to the next, specifically accounting for the drastic drop in fluid density (and thus force-producing ability) between water and air. Jumping for food requires more precision than jumping for migration or escape. Organisms ranging in size from large marine mammals and sharks (length O(10m)) to small copepods (length O(0.01m)) have developed aquatic jumping strategies compatible with their size and survival goals (e.g., prey capture, escape, mating or migration). Larger animals tend to employ burst swimming for short periods before water exit, and smaller swimming fish tend to use S- or C-start acceleration maneuvers to generate jump thrust. Even smaller organisms such as copepods exhibit jumping behaviors using unique hydrodynamic mechanisms for impulsive vortical formation. However, water escape by engineered machines has yet to be mastered. Water-to-air transitions in vehicles are typically accomplished through high-momentum, high fuel consumption, artificial jets or propellers. The synergistic multi-propulsor relationships identified from fish swimming investigations could be paradigm-shifting for the design of bioinspired multiphase vehicles. This talk will discuss how studies of freely swimming fish and flapping foils can inform jumping analysis and our understanding of fin-fin interactions in complex fish maneuvers. [Preview Abstract] |
Sunday, November 24, 2019 4:01PM - 4:14PM |
G03.00002: Sources of drag and optimizing strategies in fish employing undulatory swimming Gen Li, Dmitry Kolomenskiy, Hao Liu, Ulrike Müller, Cees Voesenek, Johan van Leeuwen, Benjamin Thiria, Ramiro Godoy-Diana Fish undulatory kinematics is not only a means to overcome drag, but also a source of it. By utilizing a computational approach that couples the Navier-Stokes equations with the equations of undulating body motion, we decomposed thrust and drag in swimming fish, and found that the scaling trend of drag during undulatory swimming follows that of a rigid three-dimensional object, while the drag magnitude is strongly influenced by the undulatory kinematics, much exceeding that of a rigid fish gliding at the same speed. By constructing a simulation-based performance map in the frequency-amplitude parameter space, we obtained the speed-specific optimal strategy that minimizes the cost of transport (CoT) during cyclic swimming. The derived optimal strategies for various types of swimmers all suggest that fish should change tail-beat frequency to control speed with a nearly constant tail-beat amplitude. Because drag during coasting is much less than that during undulatory propulsion at the same speed, properly switching between undulatory propulsion and coasting may reduce the cost of transport. We quantitatively investigated the burst-and-coast gaits that minimize CoT in transport with and without target distance , as well as in swimming at various speeds. [Preview Abstract] |
Sunday, November 24, 2019 4:14PM - 4:27PM |
G03.00003: Vorticity Generation and Arrangement Behind a Two Degree-of-Freedom Fish Model Seth Brooks, Melissa Green A two-degree-of-freedom fish model was investigated to understand the phenomenological relationship between simplified fish body kinematics and wake vortex dynamics. Its design, construction, and actuation provide control over frequency, tail (posterior half of body) angle, caudal fin to tail relative angle, and phase offset between the two angles. The frequency and phase offset were fixed for all cases in the current work while the tail and caudal fin angles were varied to create eight cases. Phase-averaged velocity data was collected beside the posterior half of the model as well as in the wake of the model. Data was obtained using stereoscopic particle image velocimetry at multiple planes along the entire span of the caudal fin. It was found that the body-generated vortices did not significantly interact with the caudal fin. The caudal fin leading edge vortex detaches from the surface sooner in cases with larger maximum tail angle. The total circulation generated at the caudal fin trailing edge was found to be sensitive to trailing edge velocity while being relatively insensitive to freestream velocity. Finally, the shedding of vortices from the caudal fin trailing edge was found to usually, but not always, coincide with periods of trailing edge deceleration. [Preview Abstract] |
Sunday, November 24, 2019 4:27PM - 4:40PM |
G03.00004: Numerical analysis of the force generation mechanism in a stingray inspired circular plan-forms Ravi Chaithanya Mysa, Pablo Valdivia Y Alvarado The effects of stingray inspired traveling wave kinematics on propulsive forces in a circular plan-form are studied in detail as part of this numerical study. Numerical flow experiments are performed at a Reynolds number of 500 on a circular plan-form for traveling waves of various amplitudes, frequencies and wave numbers. The thrust coefficient increases with increase in frequency and amplitude of wave motion. There exists a critical wave number at which the maximum thrust coefficient occurs. The magnitude of increase in thrust coefficient with increase in wave number before the critical point is greater than the magnitude of decrease in thrust coefficient with increase in wave number after the critical point. The pressure distribution on the circular plan-form is investigated in detail to understand the mechanism of force generation due to the interaction of the plan-form with the flow. At a given instant, the pressure distribution on one side of the plan-form is due to exchange of momentum between the flow and the plan-form. On the opposite side of the plan-form the pressure force is due to the edge vortex which creates suction pressure. [Preview Abstract] |
Sunday, November 24, 2019 4:40PM - 4:53PM |
G03.00005: The ground effect on anguiliform swimming performance. Mohsen Daghooghi, Uchenna Ogunka, Iman Borazjani Sea Lampreys are found in the northern and western Atlantic Ocean along shores of Europe and North America as well as in the shores of Great Lakes and nearby rivers. This species is anadromous; from their lake or sea habitats, they migrate up rivers to spawn. In other words, they specialized to efficiently swim not only in deep but also in shallow waters. Various studies have shown that certain types of fish swim close to a solid surface to reduce thrust requirements and increase efficiency as a result of interactions between the wake and the surface in steady swimming. To access the effects of a nearby substrate on the swimming performance of sea lampreys, a numerical simulation is performed to investigate how ground effects could possibly alter flow in the narrow gap between substrate and fish and influence the swimming hydrodynamics. [Preview Abstract] |
Sunday, November 24, 2019 4:53PM - 5:06PM |
G03.00006: Swimming Freely Near the Ground Leads to Flow-Mediated Equilibrium Altitudes Keith Moored, Melike Kurt, Jackson Cochran-Carney, Qiang Zhong, Amin Mivehchi, Daniel Quinn Experiments and computations are presented for a foil pitching about its leading edge near a solid boundary. The foil is examined when it is constrained in space and when it is unconstrained or freely swimming in the cross-stream direction. It was found that the foil has stable equilibrium altitudes: the time-averaged lift is zero at certain altitudes and acts to return the foil to these equilibria. These stable equilibrium altitudes exist for both constrained and freely swimming foils and are independent of the initial conditions of the foil. In all cases, the equilibrium altitudes move farther from the ground when the Strouhal number is increased or the reduced frequency is decreased. Potential flow simulations predict the equilibrium altitudes to within 3-11\%, indicating that the equilibrium altitudes are primarily due to inviscid mechanisms. In fact, it is determined that stable equilibrium altitudes arise from an interplay among three time-averaged forces: a negative jet deflection circulatory force, a positive quasi-static circulatory force and a negative added mass force. At equilibrium, the foil exhibits a deflected wake and experiences a thrust enhancement of 4-17\% with no penalty in efficiency as compared to a pitching foil far from the ground. [Preview Abstract] |
Sunday, November 24, 2019 5:06PM - 5:19PM |
G03.00007: Fluid-mediated stable equilibria for two-dimensional schools Melike Kurt, Keith Moored Fish oscillate their fins and tails and create disturbances in the form of vortical wake structures. These fish often operate in groups or collectives, which alter these structures and consequently their force production. In the 1970s, Sir James Lighthill hypothesized that for fast locomotion, hydrodynamic interactions could give rise to orderly patterns in fish collectives without the need for collective decision-making or active control mechanisms. Previous studies tested this hypothesis by studying the force equilibria in one-dimensional schools where swimmers are arranged along the stream-wise direction in in-line configurations. Here, our goal is to investigate the existence of these equilibrium points in two-dimensional schools by varying synchrony, as well as the cross-stream and stream-wise spacings between two hydrofoils. To this end, flow field analysis, as well as force measurements, will be conducted to draw a relation between the fluid-mediated forces and vortical interactions within the flow-field. [Preview Abstract] |
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