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 C09: Interact: Swimming and Flying at Moderate and High Reynolds Numbers |
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Chair: Kenneth Breuer, Center for Fluid Mechanics, Brown University Room: Ballroom I |
Sunday, November 24, 2024 10:50AM - 11:20AM |
C09.00001: INTERACT FLASH TALKS: Swimming and Flying at Moderate and High Reynolds Numbers Each Interact Flash Talk will last around 1 minute, followed by around 30 seconds of transition time. |
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C09.00002: Modeling flying formations as flow-mediated matter Christiana Mavroyiakoumou, Jiajie Wu, Leif Ristroph Collective locomotion of flying animals is fascinating in terms of individual-level fluid mechanics and group-level structure and dynamics. Here we introduce a model of formation flight that views the collective as a material whose properties arise from the flow-mediated interactions among its members. It builds on an aerodynamic model that describes how flapping flyers produce vortex wakes and how they are influenced by others' wakes. Long in-line arrays show that the group behaves as a soft, excitable "crystal" with regularly ordered member "atoms" whose positioning is, susceptible to deformations and dynamical instabilities. Perturbing a member produces longitudinal waves that pass down the group while growing in amplitude; with these amplifications even causing collisions. The model explains the aerodynamic origin of the spacing between the flyers, the springiness of the interactions, and the tendency for disturbances to resonantly amplify. Our findings suggest analogies with material systems that could be generally useful in the analysis of animal groups. |
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C09.00003: Active and Passive Damping Effects During Hummingbird Escape Maneuvers Griffin Hyde, Haoxiang Luo, Bret W Tobalske, Bo Cheng When hummingbirds detect a threat during hovering, they perform rapid body rotations in combination with high linear accelerations to escape. Fast and precise control of their body rotations is critical in such escape maneuvers. In this work, we computationally modelled the full-body aerodynamics of the hummingbird escape maneuver and identified the damping mechanisms that the birds utilize for rotation control after the top rotational velocities have been reached. We performed numerical simulations of the hummingbird for both the free-body flight and the "fixed-body" flight, where the bird's body rotation was removed and only the wing kinematics relative to the body were incorporated into the simulation. The comparison of two simulations allows us to identify the passive damping effects inherent in flapping-wing flight, e.g., the well-known flapping counter torque (FCT) that is induced when the body rotation is coupled with wing stokes. Our results show that in producing passive damping torques, the body rotation not only modifies the wings' velocities but also their effective angles of attack, an effect that is not included in the FCT. In addition to the passive damping mechanisms, we found that the bird also uses significant active damping to control the body rotations. |
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C09.00004: Effects of Wing Damage on Aerodynamic Performance and Structural Integrity in Flapping Wings Naeem Haider, Seth Lionetti, Zhipeng Lou, Chengyu Li Insect flight is a complex and highly adaptive phenomenon, particularly resilient to various forms of wing damage. Blue bottle flies exhibit remarkable flight capabilities despite sustaining injuries that compromise wing integrity. This study explores the effects of wing damage by systematically cutting the wings at various positions along the wingspan. The primary objective is to analyze how such structural impairments influence aerodynamic performance, wing deformation, and energy efficiency during flight. Using fluid-structure interaction computational models, we simulated the aerodynamic forces and structural responses of both intact and damaged wings. Our results show distinct changes in lift and drag forces depending on the extent and location of the wing damage. Additionally, damaged wings exhibited increased deformation, indicating a loss of structural stiffness and integrity. Flow visualization around the damaged wings demonstrated altered vorticity patterns and wake structures. These changes in flow structure are attributed to the disrupted aerodynamic surface and altered pressure distribution, leading to inefficient lift generation and increased turbulence. The study highlights the intricate balance between wing structure and aerodynamic performance, offering critical insights into the resilience and adaptability of insect flight. |
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C09.00005: Data-Driven Reduced-Order Modeling of a Flying Hawkmoth’s Wake Seth Lionetti, Chengyu Li Computational fluid dynamics (CFD) simulations offer precise insight into complex flow phenomena yet are often prohibitively time- and resource-intensive. To address this challenge, this study applies reduced-order modeling (ROM) to the problem of insect flight. We begin by simulating a hawkmoth's wake using an in-house immersed-boundary-method-based CFD solver. Then, dynamic mode decomposition (DMD) is used to decompose the wake into a set of time-varying modes. Finally, we employ sparse identification of nonlinear dynamics (SINDy) principles to formulate a low-dimensional model of the wake dynamics. Using these techniques, we demonstrate that the wake can be effectively modeled by a Stuart-Landau oscillator, providing a simple and interpretable representation of the complex flow dynamics as a limit cycle. This approach allows us to create a concise dynamic model of the hawkmoth's wake without relying on computationally expensive full-scale CFD simulations. Notably, our methodology produces a model that captures both transient and fully periodic wake dynamics. Furthermore, we explore the extension of this approach across multiple flight speeds, demonstrating its versatility in capturing wake dynamics across various flow conditions. The simplicity and efficiency of this ROM approach have significant implications for the design and control of bio-inspired micro-aerial vehicles (MAVs), offering a powerful tool for rapid analysis and optimization of flight performance. |
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C09.00006: Aerodynamic compensation of wing damage in houseflies Thomas Engels, Henja-Niniane Wehmann, Fritz-Olaf Lehmann Flying insects, spectacular little flapping machines with enormous evolutionary success, are an invaluable source of inspiration for an interdisciplinary community of scientists. The aerodynamic mechanisms insects use for propulsion are quite different from human-designed flying machines, and many aspects of their locomotion are not yet understood. In this talk, we will discuss the flight of the housefly (Musca domestica) with broken wings. We combine wing wear experiments, in which we study how wing damage progresses over time, with state of the art numerical simulations of the aerodynamics of flies with broken wings. The numerical simulations are done with our in-house open-source solver WABBIT (Engels et al. Commun. Comput. Phys., doi:10.4208/cicp.OA-2020-0246), which combines wavelet-based adaptivity with an efficient parallelization to exploit massively parallel supercomputers. A combination of these high-fidelity data, a simple aerodynamic model and a full-scale simulation predicts the energetic cost of flight with broken wings. In sum, the results allow us to estimate locomotor reserves of a flying fly, which provides valuable guidelines for the design of aerial robots using flapping wings for propulsion. |
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C09.00007: Evolution of flight: The Size and Energetic Constraints on Giant Dragonfly Flight Z Jane Wang Giant dragonflies (griffenflies) were the largest insects in natural history and were precursors to modern dragonflies and other insects. The largest fossils show an impressive wing lenth of 30 cm. This gigantism is correlated with the increased oxygen levels during the Permian period (300-270 million years ago). The upper limit on size depends on body form, oxygen levels, metabolic rates, and muscle energetics. I use physical arguments to predict the size range, wing motion, and flight energetics of these insects. The predicted size range encompasses the fossil records found in the US, France, and Russia. I will further present computational results on flight energetics. These physical arguments also predict the size range of other flying insects due to oxygen fluctuations during their evolutionary history. |
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C09.00008: Aerodynamic effects of varying aspect ratio of flapping wings at low Reynolds numbers relevant to the flight of tiny insects Sam Glenn, Arvind Santhanakrishnan A significant transition occurs between chord-based Reynolds number (Re) of approximately 30 and 60 for revolving elliptical wings at constant angle of attack. While significant spanwise flow, attached leading edge vortex (LEV), and separated trailing edge vortex (TEV) are observed at higher Re, diminished spanwise flow and attached LEV and TEV are observed at lower Re. The effects of aspect ratio (AR), defined herein as the ratio of wingspan squared to total wing area, have not been examined at low Re relevant to the flight of tiny insects. We experimentally measured time-varying lift and drag forces on elliptical wing models with AR of 3, 5 and 7 (identical in wing span) at Re=20, with each wing revolving through 180 degrees about a horizontal stroke plane at a constant angle of attack. The results showed that angle of attack had minimal effect on the lift coefficients. Drag coefficient increased with decreasing AR, particularly for high angles of attack. Flow field data will be presented using 2D particle image velocimetry to further investigate the effects of AR. |
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C09.00009: Agile Maneuvering: Damselfly Backward Flight and Its Aerodynamic Mechanism Jiacheng Guo, Ayodeji T Bode-Oke, Theodore LengKong, Haibo Dong Researchers have often looked to insects and small birds for inspiration to design highly maneuverable flapping-winged aerial vehicles. While considerable progress has been made in understanding the forward and turning flights of these animals, their remarkable ability to use backward flight to transition between flight modes has been largely overlooked. This study examines the body kinematics and aerodynamics of damselflies performing backward maneuvering flight. High-speed videos were captured to record damselflies in backward flight before transitioning to forward flight. A point-based reconstruction method was employed to accurately model the kinematics and deformation of the damselfly's body and wings. Using an in-house immersed-boundary-method-based (IBM) incompressible flow solver combined with the local refinement method, we accurately simulated the flow around the damselfly and its force production throughout the maneuver. Strong leading-edge vortices (LEVs) were generated on all four wings, with the LEV-induced leading-edge suction enabling effective and efficient lift and thrust production. The phase difference between the forewings and hindwings facilitated strong vortex interactions between the wings. This study provides a detailed analysis of vortex formation, wing kinematics, and their relation to the force production of the damselfly during backward maneuvers. |
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C09.00010: Positional control of an underwater vehicle using pectoral fins Pedro C Ormonde, Eric Edward Handy-Cardenas, Eva Erickson, Xiaowei He, Kenneth S Breuer Fine scale positioning and station-keeping of underwater vehicles inspired by fish locomotion requires understanding the forces generated by secondary control surfaces used to maneuver. Here, the unsteady maneuvering of a robotic fish is explored using an idealized, 2D fish body with two pectoral fins, where each fin is a rigid 2D flapping plate. Experiments in a water channel with a stationary fish are used to measure the forces generated by the fins as a function of their prescribed kinematics. Flow visualization (PIV) and numerical simulations are leveraged to characterize the flow structures. Next, a cyber-physical system with three degrees of freedom is used to experimentally study the dynamical response of the fish. Here, the fish is allowed to freely translate (surge and heave) and rotate (pitch) in the horizontal plane. We present the force and moment generation as a function of Strouhal number, amplitude and phase synchrony between the two fins, and discuss the implications for the maneuverability of underwater vehicles. |
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C09.00011: Surfing vortex rings for energy-efficient propulsion Peter J Gunnarson, John O. Dabiri Leveraging background fluid flows for propulsion has the potential to enhance the range and speed of autonomous aerial and underwater vehicles. In this work, we demonstrate experimentally a fully autonomous strategy for exploiting vortex rings for energy-efficient propulsion. First, an underwater robot used an onboard inertial measurement unit (IMU) to sense the motion induced by the passage of a vortex ring generated by a thruster in a 13,000-liter water tank. In response to the sensed acceleration, an impulsive maneuver entrained the robot into the material boundary of the vortex ring. After entrainment, the robot was propelled across the tank without expending additional energy or control effort. By advecting with the vortex ring, the robot achieved a near five-fold reduction in the energy required to traverse the tank. Using the controlled finite-time Lyapunov exponent field and corresponding Lagrangian coherent structures, we analyze and explain the initial entrainment process and the sensitivity to the starting time and position of the surfing maneuver. Additionally, linear acceleration as sensed by the onboard IMU was found to correspond with the pressure gradient of the background flow, and rotational acceleration is suggested as a method for measuring background vorticity. This work serves as a proof-of-concept demonstration of the potential for onboard inertial measurements to enable efficient interaction with background fluid flows. |
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C09.00012: Emergent behavior of autonomous group swimmers using multi-agent deep reinforcement learning Siddhartha Verma, Alejandro Alvaro, Aishwarya Sureshkumar Nair Various fish species can utilize the velocity field generated in the wakes of obstacles, and in the wakes of other swimmers, to reduce their energy expenditure. Here, we explore the hydrodynamic benefits of group swimming using two-dimensional numerical simulations of self-propelled anguilliform swimmers, coupled with multi-agent reinforcement learning. These artificial swimmers utilize a sensory input system that allows them to detect the velocity field and pressure on the surface of their body, which is similar to the lateral line sensing system. Deep reinforcement learning is used as a tool to discover optimal swimming patterns at the group level, as well as at the individual level, as a response to different objectives and flow fields. This can be useful in distinguishing various swimming patterns and their role in achieving higher speeds or efficiency, which are desirable objectives in different scenarios. The adaptations in response to changes in the surrounding flow field are also examined by training the swimmers in stationary flow, as well as uniform flow. These flow fields are representative of conditions encountered by fish in lakes and oceans (stationary flow), as well as during long-distance migration and in rivers (uniform flow). The physical mechanisms revealed can be helpful in understanding the motivation behind different swimming behaviors from a hydrodynamic and energetics standpoint. |
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C09.00013: Robotic Intervention in Fish Schools: An Innovative Method for Unveiling Collective Behavior Hydrodynamics Yu Pan, George V Lauder Collective swimming is a complex and integrated process crucial for foraging, predator avoidance, social interaction, and navigating flow environments. While observational studies in the wild and controlled laboratory settings have provided insights into fish schooling behavior, various factors such as physical laws and physiological influences are entangled, and only limited data are available on how specific factors determine individual fish behavior and collective dynamics. Inspired by previous experiments studying live fish interacting with a flapping foil, we have 3D-printed a flexible fish robot modeled after giant danio (Devario aequipinnatus). This robot mimics live fish swimming through actuation in sway and yaw directions at frequencies up to 10Hz. We conduct experiments in a circulating water channel with controlled flow speeds to investigate the interactions between the fish robot and live giant danio schools of varying sizes. Our study examines how the robotic fish with different swimming kinematics affects the collective dynamics of fish schools under varied sizes and flow conditions. Using digital particle image velocimetry (DPIV), we measure the flow field around the fish robot and the live fish school, characterizing the hydrodynamic interactions between them. Additionally, high-speed cameras coupled with machine learning-based tracking methods capture the motion and undulating kinematics of individual live fish within the school for detailed schooling dynamics analysis. By integrating the kinematic data obtained from experiments with computational fluid dynamics (CFD) simulations, we provide comprehensive flow information for the analysis of schooling physics. Our results reveal how the fish robot manipulates schooling dynamics, how live fish dynamically react to the altered flow environment introduced by the fish robot, and how fish coordinate with both their conspecifics and the artificial fish to exhibit collective behavior. |
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C09.00014: How Dynamic Damping can be Beneifical for Rapid Swimmers Orion A Roberts, Alex Sorensen, Jamie Preston, Zihan Zhang, Eric Tytell, Qiang Zhong Flexibility plays a crucial role in the dynamics of flapping propulsors. Both biological systems and robot models have demonstrated that by changing the stiffness of a flexible foil state of high thrust generation or efficient swimming can be achieved. Yet, biomimetic robots still cannot achieve the same performance as biological swimmers. Recent biology studies have revealed fish not only tune their body stiffness but also modulate damping during maneuvers. We speculate that this dynamic damping might be related to the rapid swimming capabilities observed in nature. To explore the damping effects and associated wake dynamics, we focus on a prescribed heaving, cyber-physically passive pitching hydrofoil, which can vary its stiffness and damping responses arbitrarily, allowing extensive automatic parametric sweeps. The wake structure is investigated using particle image velocimetry. Combining the two measurement methods, we offered a detailed understanding of the underlying physics of damping effects on swimming for the first time. |
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C09.00015: Stable Formations and Energetics of a Schooling Bio-Robots Keith W Moored, Tianjun Han, Pedro C Ormonde, Seyedali Sarraf, Matthew Stasolla The energy savings of fish schools have inspired previous studies to examine of the energetics of bio-robots tethered together or to a rig in a fixed formation. However, these bio-robots were not independently free-swimming like fish in a school. We present new experiments on a pair of independently free-swimming tuna-like bio-robots. The tuna-like robots are attached to independent air bearing platforms making them free-swimming in the streamwise direction. We examine the bio-robots swimming speed, potential for stable formations, and their energetics at a range of phase synchronies, lateral separation distances, and amplitudes. It is determined that the bio-robots have a stable side-by-side formation like interacting hydrofoils, yet contrary to hydrofoils the formation is stable for both in-phase and out-of-phase synchronizations. It is revealed that this stable formation is driven by a body-to-body interaction rather a fin-fin interaction. In addition, mismatched amplitudes are examined as a means for the robots to save energy while maintaining a stable formation. |
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C09.00016: ABSTRACT WITHDRAWN
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C09.00017: Cohesion of Large Groups of Self-Propelled Swimmers Mohamed Niged Mabrouk, Daniel Floryan Swimming animals gain several benefits when swimming together as a group. Crucially, the benefits of schooling can only be realized if the appropriate group structure is maintained. Using a three-dimensional far-field model of self-propelled swimmers, we examine whether passive hydrodynamic interactions alone can lead to the formation of cohesive groups of N swimmers. For N = 2, cohesive groups with several dynamical phases can form. For N > 2, subgroups of two form in some cases, while larger subgroups form in other cases. Initial misalignment of the swimmers leads them to diverge from each other when N = 2, but it can promote cohesion when N > 2. |
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C09.00018: An experimental investigation into the stride lengths and wakes of bio-inspired fins with parametrically varied planform geometries and oscillatory kinematics Justin T King, Melissa A Green The caudal fins and flukes of swimming animals may exhibit significant diversity among species in terms of planform, leading edge shape, and trailing edge shape. The current work uses experiments to investigate the self-propelled swimming speeds and stride lengths of bio-inspired pitching and heaving propulsors of varying planform shape in a recirculating water channel. Trailing and leading edge shape, as well as oscillatory kinematics, are varied for a series of bio-inspired panels with a nominally trapezoidal planform. Thirteen panel geometries were parametrically varied to facilitate investigations into specific geometric factors and their influence on swimming performance. Time-varying results obtained from particle image velocimetry at the midspan plan illustrate what wake features and behaviors are associated with optimal swimming performance and changes in oscillatory kinematics. The analysis of swimming performance and wake behaviors is discussed in the context of changes to planform shape, aspect ratio, and kinematics. The findings of the current work have implications on our understanding of the propulsor shapes found in swimming animals and also on the design of bio-inspired vehicles during conditions of constant velocity swimming. |
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C09.00019: Numerical study of maneuvering of a self-propelled undulatory batoid (Rajiform) swimmer Rohit Nuli, Ming Li, Sung Goon Park, Lian Shen Batoid fishes are characterized by their dorsoventrally flattened disk-like bodies. In this study, we focus on Rajiform (undulatory) locomotion, where swimmers generate thrust by propagating backward traveling waves along each pectoral fin. Rajiform swimmers, like stingrays, maneuver themselves by introducing an asymmetry into their swimming kinematics; this involves modifying the parameters of the traveling wave passing over each pectoral fin, including changes in amplitude, frequency, direction, and phase. Since stingray pectoral fins are key to generating thrust and maneuvering, changes to the swimming kinematics result in very dynamic maneuvers, making it essential to consider a self-propelled swimmer to study the problem of maneuvering numerically. In this study, we perform high-fidelity fluid-structure interaction simulations of self-propelled stingrays using our in-house Immersed Boundary (IB) code. We study the effectiveness and stability of these maneuvers. By investigating the hydrodynamics of these maneuvers, we aim to provide insights that can help design more efficient underwater bio-inspired robots. |
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C09.00020: Ground effects on oscillatory and undulatory batoid-inspired fins Yuanhang Zhu, Leo Liu, Qimin Feng, Tianjun Han, Keith W Moored, Qiang Zhong, Daniel B Quinn Experiments and simulations were employed to study the propulsion of batoid-inspired fins near the ground, focusing on the effect of wavenumber. Three wavenumbers were tested, ranging from oscillation (wavenumber<1) to undulation (wavenumber>1). Unlike 2D hydrofoils, which produce both suction and repulsive forces in the lateral direction, the 3D fins here produced only suction forces. These suction forces were most prominent at low wavenumbers, low ground distances, and high Strouhal numbers. Using inviscid simulations, we determined that the suction force resulted from the dominance of negative quasi-steady lift over positive wake-induced lift, with the added-mass lift staying equal to zero. Thrust generation and power consumption also increased with Strouhal number and decreased with wavenumber, but they were not as susceptible to ground effects as lift. Three-dimensional flow measurements demonstrated that fins employing oscillatory motion generated stronger trailing-edge vortices and exhibited wider wakes due to higher wave speeds, making them more sensitive to ground presence as compared to their undulatory counterparts. Finally, we analyzed the efficiency, instantaneous lift, and angle of attack of the fins to provide insights into batoid-like propulsion of biological and engineering systems. |
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C09.00021: Flapping to the Surface: Free Surface Effects on a Manta Ray-Inspired Panel Ben Darden, Christine Gilbert Taking inspiration from manta rays - naturally great swimmers - can allow human-made devices to operate with greater efficiency. In this talk, a shape-changing panel is used to model a manta ray fin, by two rows of actuating tubes. Unsteady flapping motions and shape change of the panel will be implemented in calm water at different depths from the free surface. Forces, panel shape, input motions, and fluid features will be measured and reported. In this phase of experiments, the shape change of the panel was prescribed and then the panel was subjected to an unsteady flapping motion. With only one row of tubes actuated, the maximum force decreased as the panel was flapped at increasing depths from the free surface. However, when subjected to dual actuation, or an increase in panel stiffness, the maximum force stayed relatively constant at increasing depths. At close distances to the free surface, the tip of the panel is attracted to the free surface due to low pressure, which is seen in a greater deflection toward the free surface. The knowledge gained from this study will be extended by testing a manta ray model in a towing tank where both horizontal and vertical motions can be prescribed along with shape change. |
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C09.00022: Flow Structures Developed by Bio-Inspired Robotic Sea Lion Flippers of Varied Effective Flexibility Ian William Moss, Megan C. Leftwich Sea lions use a combination of lift and drag-based propulsion to generate thrust with their foreflippers. Previous research analyzed the flow structures arising from a single robotic foreflipper at varied constant angular velocities and effective flexibilities through a simulated clapping motion. This revealed that the predominant flow structure is a thrust-generating vortex the strength of which is determined by the combination of effective flexibility and angular velocity. The vortex forms at the dorsal side of the flipper, grows in size until the flipper contacts a flat plate representing the sea lion’s body, and then convects in the opposite direction of the sea lion’s forward motion, producing thrust. The flow structures can be compared non-dimensionally as a function of velocity and flexibility, best characterized by an effective lag in the flow structures produced. Here, we characterize this non-dimensional relationship while additionally analyzing the effects of acceleration on the flow structures produced, closely resembling the true clap-like motion that sea lions exhibit. We also aim to understand how effective flexibility affects the flow structures during porpoising, another common swimming maneuver used by sea lions, where the foreflippers are used more passively for stabilization rather than propulsion. |
Sunday, November 24, 2024 11:20AM - 12:50PM |
C09.00023: INTERACT DISCUSSION SESSION WITH POSTERS: Swimming and Flying at Moderate and High Reynolds Numbers After each Flash Talk has concluded, the Interact session will be followed by interactive poster or e-poster presentations, with plenty of time for one-on-one and small group discussions. |
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