Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session L9: Swimming IVBio Fluids: External
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Chair: Mohsen Daghooni, University at Buffalo - SUNY Room: 502 |
Monday, November 20, 2017 4:05PM - 4:18PM |
L9.00001: How lampreys swim in nature? Pressure field and the mechanisms of propulsion Iman Borazjani, Mohsen Daghooghi We performed self-propelled, large-eddy simulations of lampreys based on the recent experiments on live lampreys. Using two undulation types (traveling and standing waves), the pressure field around the body is visualized and physical principles of eel-like swimming are discussed.~ Visualization of pressure does not show any evidence in support of the suction-based theory, recently proposed as the prime mechanism of thrust generation for eel-like swimming.~ On the contrary, our results for surface pressure are in good agreement with theoretical predictions of Lighthill's elongated body theory for deformable bodies.~ [Preview Abstract] |
Monday, November 20, 2017 4:18PM - 4:31PM |
L9.00002: Flow-structure Interaction Modeling of a Fish Caudal Fin during Steady Swimming Geng Liu, Biao Geng, Xudong Zheng, Qian Xue, Haibo Dong It's widely thought that the flexibilities of fish fins play critical roles in propulsive performance enhancement (such as thrust augment and efficiency improvement) in nature. In order to explore the formation mechanisms of the fish fin's flexible morphing and its hydrodynamic benefits as well, a high-fidelity flow-structure/membrane interaction modeling of the fish caudal fin is conducted in this work. Following the realistic configuration of the fish caudal fin, a thin membrane supported by a series of beams is constructed. The material properties of the membrane and the beams are reversely determined by the realistic fin morphing obtained from the high-speed videos and the high fidelity flow-structure interaction simulations. With the accurate material property, we investigate the interplay between structure, kinematics and fluid flow in caudal fin propulsion. Detailed analyses on the relationship between the flexural stiffness, fin morphing patterns, hydrodynamic forces and vortex dynamics are then conducted. [Preview Abstract] |
Monday, November 20, 2017 4:31PM - 4:44PM |
L9.00003: Kinematics and Hydrodynamics of Burst-and-Coast Strategy in Carangiform Swimming Pan Han, Haibo Dong, Valentina Di Santo, George Lauder In this work, burst-and-coast swimming hydrodynamics of a trout is studied using a combined experimental and computational approach. The associated kinematics is reconstructed from the output of a high-speed photogrammetry system. The hydrodynamic performance and wake structures are then investigated using an in-house immersed-boundary-method based flow solver and compared with those found in steady undulatory swimming. Results have shown that the carangiform swimmer uses a completely different trust producing strategy when conducts burst-and-coast swimming. Comparing to steady swimming, the trunk curvature of the fish has increased twofold during the burst phase. As a result, it contributes about 15{\%} of total trust during the swimming. Results have also shown that the thrust produced by the caudal fin has increased by tenfold during burst swimming due to larger flapping amplitude and pitching angle. Vortex dynamics analysis has shown that unlike the steady swimming, vortex rings formed during burst swimming result in a stronger downstream jet, which suggests a new thrust enhancement mechanism in carangiform swimming. [Preview Abstract] |
Monday, November 20, 2017 4:44PM - 4:57PM |
L9.00004: Low Dimensional kinematic models and hydrodynamic performance of a Trout in steady swimming Junshi Wang, Yan Ren, Geng Liu, Haibo Dong, Valentina Di Santo, George Lauder Highly flexible body undulations are commonly observed in fish swimming. However, quantifying hydrodynamic advantages of body flexion remains unexplored in live fish swimming. In this work, a combined experimental and computational approach will be introduced to study the hydrodynamic role of body flexibility in a trout's steady swimming. High-speed photogrammetry system and 3D model reconstruction technique are used together to measure the kinematics of body and fins with extraordinary details. A singular value decomposition (SVD)-based model reduction tool is developed to extract the dominant kinematical components of the entire fish for kinematics analysis and computational modeling. An immersed-boundary-method (IBM)-based computational fluid dynamics solver is then used to simulate the corresponding unsteady flows in all their complexity. Vortex dynamics and hydrodynamic benefits of different kinematical components are then studied. The methods and resulted findings from this work are expected to bring new insights on the design of next generation bio-inspired autonomous underwater systems. [Preview Abstract] |
Monday, November 20, 2017 4:57PM - 5:10PM |
L9.00005: Combining the Vortex Particle-Mesh method with a Multi-Body System solver for the simulation of self-propelled articulated swimmers Caroline Bernier, Mattia Gazzola, Renaud Ronsse, Philippe Chatelain We present a 2D fluid-structure interaction simulation method with a specific focus on articulated and actuated structures. The proposed algorithm combines a viscous Vortex Particle-Mesh (VPM) method based on a penalization technique and a Multi-Body System (MBS) solver. The hydrodynamic forces and moments acting on the structure parts are not computed explicitly from the surface stresses; they are rather recovered from the projection and penalization steps within the VPM method. The MBS solver accounts for the body dynamics via the Euler-Lagrange formalism. The deformations of the structure are dictated by the hydrodynamic efforts and actuation torques. Here, we focus on simplified swimming structures composed of neutrally buoyant ellipses connected by virtual joints. The joints are actuated through a simple controller in order to reproduce the swimming patterns of an eel-like swimmer. The method enables to recover the histories of torques applied on each hinge along the body. The method is verified on several benchmarks: an impulsively started elastically mounted cylinder and free swimming articulated fish-like structures. Validation will be performed by means of an experimental swimming robot that reproduces the 2D articulated ellipses. [Preview Abstract] |
Monday, November 20, 2017 5:10PM - 5:23PM |
L9.00006: Role of body surface pressure and kinematics in fish turning John Costello, Sean Costello, John Dabiri, Megan C. Leftwich Experiments on freely swimming zebrafish were conducted to study the relative contributions to angular acceleration from both the induced pressure field in the fluid surrounding the animal as well as changes in the body moment of inertia due bending during turning maneuvers. PIV-based pressure measurements indicated that turning is initiated by subtle changes to body posture that create large pressure gradients at the head and tail of the animal. The angular turning motion that results from this pressure-based torque is amplified by the animal bending, which reduces the body moment of inertia during the turn. The demonstrated ability to decouple torque generation and body kinematics, using a combination PIV-based pressure measurements and image-based inertia measurements, can facilitate exploration of maneuvering dynamics in a broader range of swimming species, including a search for possible convergent maneuvering strategies that might be common among aquatic animals. [Preview Abstract] |
Monday, November 20, 2017 5:23PM - 5:36PM |
L9.00007: Amplitude Effects on Thrust Production for Undulatory Swimmers Brittany Gater, Javid Bayandor Biological systems offer novel and efficient solutions to many engineering applications, including marine propulsion. It is of interest to determine how fish interact with the water around them, and how best to utilize the potential their methods offer. A stingray-like fin was chosen for analysis due to the maneuverability and versatility of stingrays. The stingray fin was modeled in 2D as a sinusoidal wave with an amplitude increasing from zero at the leading edge to a maximum at the trailing edge. Using this model, a parametric study was performed to examine the effects of the fin on surrounding water in CFD simulations. The results were analyzed both qualitatively, in terms of the pressure contours on the fin and vorticity in the trailing wake, and quantitatively, in terms of the resultant forces on the fin. The amplitude was found to have no effect on the average thrust during steady swimming, when the wave speed on the fin was approximately equal to the swimming speed. However, amplitude was shown to have a significant effect on thrust production when the fin was accelerating. This finding suggests that for undulatory swimmers, amplitude is less useful for controlling swimming speed, but can be used to great effect for augmenting thrust during acceleration. [Preview Abstract] |
Monday, November 20, 2017 5:36PM - 5:49PM |
L9.00008: The Influence of Drag on the Relation Between Swimming Number and Swimming Speed. David Gross, Mederic Argentina, Yann Roux The choice of gait parameters used by swimmers has been the subject of considerable research. The recent work of Gazzola et al. (2014) showed that swimmers follow a relation between the viscosity, the~input parameters of length, tailbeat frequency and amplitude by way of a new non-dimensional swimming number Sw and the resulting Reynolds number Re that they swim at. The momentum balance leads to a 4/3 power relation between Sw and Re at moderately high Reynolds number and a linear relation between Sw and Re in the turbulent regime. We performed numerical simulations of a swimmer submitted to an imposed deformation and a resolved rigid body motion. A 2D unsteady, inviscid vortex panel method with vortex particle wake approach is used to represent the swimmer and its wake. The method was validated against the analytic solution of an impulsively started foil and a purely heaving foil. The vortex panel method is inviscid by its nature, but with an added viscous drag equivalent to a flat plate yields excellent agreement with the scaling laws observed by Gazzola et al. and 2D URANS results in both flow regimes The influence of Re dependent and independent drag coefficients was studied along with the limit of zero added drag. [Preview Abstract] |
Monday, November 20, 2017 5:49PM - 6:02PM |
L9.00009: Harnessing wake vortices for efficient collective swimming via deep reinfrcement learning Siddartha Verma, Guido Novati, Petros Koumoutsakos Collective motion may bestow evolutionary advantages to a number of animal species. Soaring flocks of birds, teeming swarms of insects, and swirling masses of schooling fish, all to some extent enjoy anti-predator benefits, increased foraging success, and enhanced problem-solving abilities. Coordinated activity may also provide energetic benefits, as in the case of large groups of fish where swimmers exploit unsteady flow-patterns generated in the wake. Both experimental and computational investigations of such scenarios are hampered by difficulties associated with studying multiple swimmers. Consequentially, the precise energy-saving mechanisms at play remain largely unknown. We combine high-fidelity numerical simulations of multiple, self propelled swimmers with novel deep reinforcement learning algorithms to discover optimal ways for swimmers to interact with unsteady wakes, in a fully unsupervised manner. We identify optimal flow-interaction strategies devised by the resulting autonomous swimmers, and use it to formulate an effective control-logic. We demonstrate, via 3D simulations of controlled groups that swimmers exploiting the learned strategy exhibit a significant reduction in energy-expenditure. [Preview Abstract] |
Monday, November 20, 2017 6:02PM - 6:15PM |
L9.00010: How swimming near a curved body could improve bio-inspired propulsion Ruijie Zhu, Junshi Wang, Haibo Dong, Hilary Bart-Smith, Daniel Quinn A simplified model is proposed to study the advantages of fish schooling. Our model predicts that fish can gain thrust and efficiency by swimming close to each other. Sinusoidal pitching motion is prescribed to a rigid airfoil to mimic a flapping caudal fin, and a rigid cylinder is placed nearby to mimic the curved body of another fish. Using Theodorsen's theory for a pitching airfoil, we estimate the thrust and power coefficient of the airfoil at various positions relative to the cylinder. We also explore the effect of the airfoil's pitching frequency, pitching amplitude, and size relative to the cylinder. Various combinations of those parameters are simulated using an immersed boundary method. Analytical and computational results are compared to evaluate the effectiveness of our fish schooling model. Our results offer new insights into the fluid physics of multi-body interactions and the hydrodynamics of fish schooling. [Preview Abstract] |
Monday, November 20, 2017 6:15PM - 6:28PM |
L9.00011: Schooling of self-propelled flexible fins Sung Goon Park, Hyung Jin Sung A fish can gain hydrodynamic advantages from being a member of a school. Inspired by fish schooling in nature, a two-dimensional simulation was performed for self-propelled flexible fins in four configurations; tandem, diagonal, triangular, and diamond configurations. The flow-mediated interactions between the flexible fins were considered by using an immersed boundary method. A heaving motion was prescribed on the leading, and other posterior parts passively fluttered. In the present self-propelled system, the schooling structures were dynamically determined, and the stable configurations were spontaneously formed and maintained purely by the hydrodynamic interactions. The swimming speed of the schooling fins was almost the same to the isolated fin. The input power was largely dependent on the schooling structure and the local positioning of the members within the structure. The input powers of the following fin in the stable tandem and diagonal configurations are lower by 14{\%} and 6{\%} respectively than that of the leading fin. The fins swimming in the second row in the triangular or diamond configuration experienced an increased input power by 5{\%} than the leading fin. The following fin in the diamond configuration reduced the input power by 23{\%} than the leading fin. [Preview Abstract] |
Monday, November 20, 2017 6:28PM - 6:41PM |
L9.00012: Experimental study on the effects of trailing edge geometry on the propulsive performance and wake structure of bio-inspired pitching panels Justin King, Melissa Green Force measurements and stereoscopic particle image velocimetry (SPIV) were used to characterize the propulsive performance and three-dimensional wake structure of rigid, acrylic pitching panels with various trailing edge geometries. Experiments were carried out on multiple panels with bio-inspired planforms that were pitched about their leading edge. A trapezoidal panel geometry with a straight trailing edge was chosen as a baseline case, and deviations from a trapezoid were studied using panels with either a concave or convex trailing edge Previous work by van Buren \textit{et al}. (Physical Review Fluids, 2017) has established that parameters such as coefficient of thrust and propulsive efficiency can be affected by changes in the trailing edge shape of pitching panels. In the current work, SPIV data were collected across the spanwise extent of the wake, and it is demonstrated that spanwise vortices are organized to form a reverse von Karman vortex street across much of the spanwise extent of the wake. The spanwise vortices are oriented in accordance with the trailing edge shape, i.e. a concave trailing edge sheds spanwise vortices that are bent inwards while a convex trailing edge sheds spanwise vortices that are bent outwards. The SPIV results also provide further insight into the three-dimensional wake behavior and structure as it relates to propulsive performance. [Preview Abstract] |
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