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 C33: Interact: Aerodynamics from Seeds to Metamaterials |
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Chair: Tim Colonius, Caltech Room: Ballroom B |
Sunday, November 24, 2024 10:50AM - 11:20AM |
C33.00001: INTERACT FLASH TALKS - Aerodynamics from Seeds to Metamaterials Each Interact Flash Talk will last around 1 minute, followed by around 30 seconds of transition time. |
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C33.00002: Extending the Hele-Shaw Analogy: Magnetic Fields Induce Circulation Kyle Ian McKee, John W M Bush Viscously-dominated flow between two closely-spaced plates is described by two-dimensional potential flow according to the standard Hele-Shaw approximation. When driven exclusively by pressure, the class of realizable potential flows is highly restricted: only flows with exactly zero circulation are possible. For example, the Hele-Shaw experiments presented in Van Dyke's famous Album of Fluid Motion clearly illustrate this zero-circulation restriction. In the present work, we demonstrate how the Hele-Shaw cell can be used to capture flows with circulation - |
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C33.00003: Compressibility-Inducted Hysteresis in Upswept Afterbody Flows Chitrarth Prasad, Datta V Gaitonde A freestream-aligned cylinder with an upswept base is a commonly used canonical surrogate to study military cargo aircraft fuselage wakes. Recent investigations with near-incompressible flow have shown the existence of two types of wakes depending on the upsweep angle: a “vortex-pair” (VP) dominated state and a “fully separated wake” (FSW), with drastic drag characteristics. This investigation aims to delineate the effects of compressibility on the wake of a cylindrical aft body with a 45° upsweep by performing well-resolved large eddy simulations at Mach numbers 0.1, 0.3, and 0.5. At Mach 0.1, the wake exhibits typical VP characteristics observed in experiments. Increasing the Mach number to 0.3 shifts the VP formation downstream due to a larger recirculation region near the start of the basal upsweep. Further increasing the Mach number transitions the flow to an FSW state, similar to observations with changes in upsweep angle at incompressible speeds. Additionally, the flow exhibits hysteresis with Mach number—the FSW state persists even when the Mach number is reduced back to 0.1. The FSW regime features larger but more uniform low-pressure regions on the base, resulting in lower drag than the VP regime. |
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C33.00004: The Aerodynamics of Spinning Seed Flight Joe L Hesse-Withbroe, Dwight L Whitaker Ruellia ciliatiflora is a perennial herb whose fruits explode and launch their thin disk-shaped seeds over 6 m with a backspin of up to 1660 Hz. |
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C33.00005: Bioinspired Slotted Wingtips as Flight Control Devices for Airborne Wind Energy Harvesting Kites Hannah M Wiswell, Aimy Wissa Airborne Wind Energy Harvesting (AWEH) systems offer improved harvesting strategies over ground-based wind energy systems due to increased wind velocity and reduced boundary layer effects at high altitudes. One example of an AWEH system is Toyota’s Mothership, a multifunctional kite platform that requires control authority to perform energy-extraction maneuvers at high altitudes. The Mothership cannot support traditional flight control devices due to its lightweight and flexible fabric-made skin. Birds fly adeptly in a wide range of altitudes and offer a variety of flight control solutions suited for light and flexible materials. Bird wings contain multiple feather groups that enhance birds’ control authority and maneuverability. One feather group, the slotted primary feathers near the wingtip, has been shown to alter aerodynamic forces, making it a viable flight control device. In this presentation, we explore the feasibility of implementing bioinspired wingtips on the Mothership for increased control authority. More specifically, we conducted wind tunnel experiments at Re = 2 x 105 and acquired Particle Image Velocimetry (PIV) measurements to evaluate various bioinspired slotted wingtip configurations on a scaled semi-span Mothership wing. Results show that the wingtips significantly modulate lift and drag, allowing for changes in moments and increased maneuvering capabilities. |
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C33.00006: Covert-Inspired Flaps as Flight Control Devices During Dynamic Pitching Maneuvers Diaa A Zekry, Aimy Wissa Small-scale Uncrewed Arial Vehicles (UAVs) have become increasingly important for both civil and military operations over the past decade. However, their flight capabilities remain limited during demanding maneuvers such as landing, takeoff, and high-pitch rate maneuvers. In contrast, birds perform similar maneuvers with relative ease, partially due to feather systems, such as covert feathers. Previous research by the authors has demonstrated that covert-inspired flaps can be used for flight control in steady-state flight conditions. This study expands our understanding of covert-inspired flaps as flight control devices by examining their effectiveness during dynamic pitching maneuvers. We conducted wind tunnel experiments and measured the aerodynamic forces and moments along with the velocity and vorticity field using time-resolved Particle Image Velocimetry (PIV) on a two-dimensional wing section with covert-inspired flaps mounted on the suction and pressure sides. Results quantify the effectiveness of covert-inspired flaps during a dynamic versus static flight maneuver. Our findings are further supported by data-driven models, and we provide recommendations for the implementation of these flaps on UAVs. |
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C33.00007: Stability in Flapping Flight for Two Different Robotic Flappers Rónán Gissler, Santiago Romo, Kiera Fullick, Oliver Sand, Alice Cannon, Victoria Herrera, Kenneth S Breuer Passive stability has important implications for maneuverability during flight. To better understand bird and bat flight, and to aid in the development of controlled flight in flapping-wing drones, we characterize the static longitudinal stability of two robotic flapping systems operating in different parameter spaces. One flaps at high frequencies (~10 Hz) with light flexible wings (~0.5 grams) while the other flaps at moderate frequencies (~5 Hz) with heavier rigid wings (~10 grams). For each system, we mounted the robot in the wind tunnel test section and recorded triaxial forces and moments over a range of wind speeds, flapping frequencies, and pitch angles. Phase- and cycle-averaged data are recorded and used to assess static longitudinal stability as a function of flight kinematics, body and wing geometry. The results are compared with a quasi-steady blade element model and areas of agreement and disagreement are identified and explained. |
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C33.00008: Experimental investigation of leading-edge vortex dynamics for a flapping flat plate with varying Rossby number Yekaterina Goodwin, Georgios Rigas, Jonathan F Morrison Leading-edge vorticity (LEV) generation is a key mechanism for delayed stall in flapping species, promoting flow attachment at high angles of attack. Understanding of such mechanisms can be applied to flapping wing MAVs and unsteady aerodynamic control. Experimental investigation of flapping flight is challenging due to the difficulty of working with live specimens and building robotics capable of performing complex wing stroke paths. We present a novel flapping flight experiment using a programmable 6-axis industrial robot to actuate a flat plate inside a wind tunnel. This allows us to mimic complex wing kinematics and control centripetal and Coriolis accelerations programmatically. Three canonical flapping procedures in forward flight, with varying Rossby number and Re=15,000, have been captured using time-resolved stereo particle image velocimetry (PIV) at 3 spanwise planes. We use proper orthogonal decomposition (POD) to understand the spectral properties of the resulting flow dynamics, in order to investigate LEV shedding versus bursting dynamics. |
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C33.00009: Pitch Optimization via a Learning Algorithm (POLA) for an Aerial Single-Rotor System Meredith L Hooper, Morteza Gharib
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C33.00010: Aerodynamic super model and universal flight simulator Olivia Pomerenk, Leif Ristroph Birds glide, plant seeds bound, falling leaves flutter, and paper sheets tumble. Can all these behaviors be accounted for by a single model? This talk is about our quest to build an all-inclusive aerodynamic model and flight simulator. The main achievement is that our quasi-steady dynamical modeling proves to be unreasonably effective at accounting for steady and unsteady flight modes. We reproduce and explain many past observations and predict new behaviors yet to be explored. The model should be generally applicable to thin wings at intermediate Reynolds numbers, and we foresee many applications for motions in arbitrary fluids, both in understanding biological locomotion as well as for designing biomimetic flying and swimming vehicles. |
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C33.00011: Flow-Induced Responses of Kirigami-Patterned Sheets Placed in Fluid Flow Adrian G Carleton, Yahya Modarres-Sadeghi We present experimental observations of flow-induced structural responses and various wake topologies generated by systematically adjusting the cut geometries of kirigami patterned sheets when placed in a fluid flow. It has been shown previously that the various categories of kirigami patterns cause a variety of static and dynamic responses in flexible sheets, from smooth and steady large-scale elongations, to buckling and flutter. This in turn creates significantly varied patterns in the downstream flow. These behaviors are not just functions of the incoming flow velocity and category of kirigami pattern, but also of the specific dimensions of the cuts in each category. This study examines the changes in the critical values associated with the onset of various structural responses as the cut geometry is varied. |
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C33.00012: Flow-Induced Buckling of a Bistable Structure in Uniform Flow Leixin Ma, Alejandra Hernandez Escobar Recent developments in soft materials have enabled the design of bistable, flexible structures. We explore the snap-through buckling process of these bistable structures driven by fluid flows, modeling the fluid-structure interaction coupling via the Arbitrary Lagrangian-Eulerian method. In the first scenario, three flexible plates with varying geometries and no initial stress are subjected to fluid-driven motion at different flow speeds. We analyze the structural deformation patterns, hydrodynamic force distributions, and fluid dynamics patterns during the snap-through buckling process. We identify the Cauchy number as a key dimensionless parameter governing bistable structures' snap-through buckling and structural strain energy storage. Predictive models for the structural dynamics' dimensionless strain energy and rise time were developed. Additionally, we examine how vortex shedding, associated with the hydrodynamic lift force, affects the structural strain energy. We also find that bistable structures exhibit larger steady-state deformation than mono-stable structures in the same flow conditions, suggesting that structural bistability significantly influences fluid-structure interaction. |
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C33.00013: Investigating flow-induced vibrations in flexible cantilevers using hybrid modal and graph neural network analysis Shayan Heydari, Rajeev Jaiman, Rui Gao This study presents a hybrid modal and graph neural network analysis to investigate flow-induced vibrations (FIVs) in long flexible cantilevers. Utilizing high-fidelity numerical simulations based on variational finite-element methods and a novel deep learning-based graph neural network reduced-order model (GNN-ROM), we examine the coupled dynamics of the cantilever under hydrodynamic interference. The flow equations are formulated within an arbitrary Lagrangian-Eulerian (ALE) framework, accounting for the structure's moving boundaries. The fluid-structure interface is managed through a partitioned iterative scheme, ensuring stable coupling of the incompressible Navier–Stokes equations with a low-mass flexible structure experiencing strong inertial effects from the surrounding flow. The integration of GNN-ROMs aims to enhance predictive capabilities by leveraging graph-based representations of the fluid-structure system. Within the ALE framework, the model employs a multi-layer perceptron to evolve mesh displacements and a hypergraph neural network to forecast fluid states based on the current system state. Our findings demonstrate that the model can learn from high-fidelity spatio-temporal simulation data to provide stable and accurate roll-out predictions with reduced computational cost. The results of this study offer implications for design optimization and the development of physics-based digital twins in fluid-structure interaction domains. |
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C33.00014: Flexible structures reconfigure and manipulate vortex rings to reduce drag Mrudhula Baskaran, Mathias Dufresne-Piché, Karen Mulleners Extreme weather conditions have become increasingly frequent in recent years, damaging rigid infrastructure like buildings and bridges. Plants resist uprooting in such weather conditions by streamlining themselves and reducing their projected area in the flow. Integrating flexible components into infrastructural design could allow them to withstand adverse weather better. We study the drag reduction and deformation of flexible radially cut disks that are translated vertically through water. We use temporally and spatially resolved velocity field measurements to quantify the properties of the vortex ring that forms on the leeward side of the flexible disks. The net entrained fluid volume vortex and the core vortical volume are reduced for deforming disks due to streamlining. The vortex consequently achieves a more uniform vorticity distribution, given by a lower non-dimensional energy. The more uniform vorticity distribution is related to a smaller pressure drop in the core, resulting in drag reduction. Using the vortex panel method we also model the drag reduction and deformation of the flexible disks. The model is validated experimentally and predicts the reduced drag of flexible structures based on the deformed shape and the incoming flow conditions. |
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C33.00015: Flow-induced oscillations of pitching plates using a cyber-physical experimental setup Winthrop Townsend, Cecilia Huertas-Cerdeira Fluid-structural interactions between elastically mounted pitching plates and uniform flow commonly produce instabilities, large amplitude limit cycle oscillations (LCOs) and chaos within certain flow regimes. The abovementioned behaviors are an academic sandbox for unsteady aerodynamic and aeroelastic research. Recent advancements in data-driven methods make setups capable of interacting with algorithms and producing large datasets increasingly necessary. |
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C33.00016: Three-Dimensional Effects in Transonic Wing Flutter: Insights from Direct Numerical Simulations Jacob M Turner, Jung-Hee Seo, Rajat Mittal Aeroelastic wing flutter poses a persistent challenge for high-performance aircraft, especially in the transonic regime, where the critical flutter speed can decrease due to the "transonic dip." Additionally, aerodynamic instabilities and non-linear damping, often caused by shock formations, can lead to limit-cycle oscillations that fatigue the aircraft and affect targeting and pilot comfort in military applications. To address these issues, a deeper understanding of shock-fluid interactions is needed. In this presentation, we consider a three-dimensional NACA0012 wing which encounters shock-stall flutter at a Reynolds number of 10,000 and Mach number of 0.7. Direct numerical simulations are based on a high-order immersed boundary code utilizing prescribed sinusoidal motion. The main aim of this study is to examine how three-dimensional shock and flow features impact energy extraction mechanisms, compared to previous two-dimensional results. Spanwise incoherence, changes in shock formation and shock trajectory are shown to influence the predicted flutter boundary. Futhermore, it is found that the assumption of two-dimensional flow results in secondary energy extraction mechanisms not observed in three dimensions. |
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C33.00017: Computational Investigation of Cambered Blades and Virtual Camber in Cross-Flow Turbines Caelan C Consing, Ari S Athair, Owen Williams, Jennifer A. Franck This research computationally investigates how cambered blades interact with the virtual camber induced in cross-flow turbine blades. Most cross-flow turbines use uncambered airfoils, likely due to the symmetries in the change of angle of attack over a complete rotation. Unlike axial-flow turbines, flow is curvilinear relative to the rotating airfoil, so an equivalent airfoil in rectilinear flow has virtual camber, changing the lift produced and relative angle of attack. In this study, single-bladed turbines with camber of up to ±3% are simulated using URANS and LES models for a range of tip-speed ratios and chord-to-radius ratios. Results are validated against experimental performance and PIV data. It is shown that camber affects the turbine performance at different parts of the cycle, depending on the direction of concavity of the camber line. This is due to camber augmenting both the lift produced by the blade and the timing of leading-edge vortex formation. It is also shown that the effects of camber are dependent on tip-speed ratio and chord-to-radius ratio, since these are the main parameters that influence the virtual camber effect. The results of this work may be used to improve the geometry of cross-flow turbines for optimal performance and control strategies. |
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C33.00018: A framework for integrating phononic materials in aerodynamic flows Arturo Machado Burgos, Sangwon Park, Nicholas D OBrien, Vinod Ramakrishnan, Kathryn H Matlack, Andres Goza There is growing interest in integrating phononic metamaterials—materials with unique frequency-dependent properties arising from their periodic structure—into passive, adaptive flow control paradigms. To fully harness these structures in the intended control aim, clear methodologies must be developed to meaningfully quantify the fluid-structure interplay, including (i) identifying what canonical phononic material models can be utilized that enable interaction between key phononic material behaviors and flow processes such as vortex shedding, (ii) synthesizing dimensionless FSI parameters that allow for systematic tuning of phononic material behaviors relative to flow processes. In the spirit of addressing these questions, we consider an aerodynamic system equipped with a compliant surface whose motion is governed by a phononic material diatomic chain. We explore "ungrounded" and "grounded" configurations and discuss their relevance for point (i). We also introduce dimensionless parameters that relate key phononic material behaviors such as truncation resonance frequency, decay rate, and static structural stiffness to key flow behaviors such as vortex shedding timescales and mean lift on the compliant portion of the airfoil. This proposed approach enables a systematic assessment of the fluid-structure interaction for this phononic material-equipped system, and is a building block for enhancing aerodynamic performance through the strategic use of phononic materials. |
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C33.00019: Span-distributed Coverts-inspired Flow Control Devices Ahmed K Othman, Aimy Wissa The coverts are contour feathers that cover the upper and lower surfaces of bird wings. Studies in biology suggest that upper wing coverts act as aeroelastic flow control devices to control flow separation and mitigate stall. Previous studies by the authors show that torsionally hinged coverts-inspired flaps mounted at different chord-wise locations on the suction side of a 2D airfoil and a 3D finite wing can enhance lift post-stall by up to 20% in both cases at a Reynolds number of 200,000. In these studies, the flaps covered the entire span of the wing, neglecting the span-wise spatial distribution of the flap. In this study, we investigate the effect of the span-wise length and distribution of covert-inspired flaps on the post-stall aerodynamics of a finite wing with an aspect ratio AR = 4.6 at a Re of 200,000. This aspect ratio was chosen due to its biological relevance, especially for birds of prey that fly at a similar Reynolds number range. More specifically, using wind tunnel experiments and time-resolved PIV, we will examine the fluid-structure interaction mechanisms of a rectangular wing with suction side span-distributed flaps. Results will show the effects of changing the hinge stiffness, flap inertia, and flap location of multiple span-distributed flaps on the aerodynamic performance of the wing post-stall and tall propagation. Moreover, we will examine the effect of the 3D flow field (i.e. spanwise flow and wingtip vortices) on the deployment dynamics of the flaps, especially how the flap behavior changes as a function of its location along both the chord and span. |
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C33.00020: Measurement of flow instability control with acoustic metamaterials Jensen McTighe, Jason M Dahl, Osama Bilal, Melanie Keogh Phononic crystals and acoustic metamaterials (AMs) embedded into flat plate surfaces have previously been demonstrated theoretically to delay (or speed up) the onset of laminar-to-turbulent boundary layer transition by attenuating (or strengthening) Tollmein-Schlicting waves. Metamaterials can be advantageous for uses in flow control as they offer a passive control method that can be engineered independently without needing a priori fluid structure interactions simulations. An AM was designed to attenuate wave instabilities with a target frequency of 75 Hz. The AM was embedded into a flat plate and a circular cylinder was placed upstream in a current to generate oscillatory flow instabilities propagating in the wake of the cylinder near the flat plate. The effectiveness of the material to attenuate the artificially introduced wake instability was evaluated over a range of cylinder positions, flow speeds, and wave instability frequencies using measurements made with 2D-particle image velocimetry. It was found that the AM could attenuate instabilities at the target frequency while amplifying certain frequencies outside of the stop band, effectively increasing the vortex shedding frequency of the cylinder. This observation appears to be similar to lock-in behavior in vortex-induced vibrations, where the natural frequency of a mechanical system can alter the natural vortex shedding frequency behind a cylinder. These results are particularly significant because this is possibly the first time flow control behaviors have been observed by using an AM through physical experimentation, validating their use as passive flow control devices. |
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C33.00021: Observations of the mitigation of reversing flow within a separating turbulent boundary layer through flexible shortfin mako shark scales Amy W Lang, Leonardo M Santos, Andrew James Bonacci, Redha Wahidi A turbulent boundary layer in the presence of an adverse pressure gradient sees flow reversal first occurring within the low-speed streaks close to the wall. Previous research has demonstrated that the flexible scales found on the skin of the shortfin mako can respond to this reversing flow, be passively actuated and mitigate this flow reversal as a primary mechanism to control flow separation. To further test this bio-inspired flow control mechanism, both real shark skin samples and 3D printed models of these flexible scales (designated MAKO models) have been tested in in a water tunnel using DPIV for a tripped turbulent boundary layer subjected to an adverse pressure gradient induced by the presence of a rotating cylinder. The real shark skin scales measure approximately 200 microns in crown length, while the MAKO models were manufactured at both 15 and 20 times the size of real shark scales. The flow has been analyzed in planes parallel to the wall to visualize the formation of the low-speed streaks and study the formation of flow reversal within these streaks for both a smooth wall and over the MAKO models. Specific examples of the mitigation of flow reversal by both the MAKO models and real shark skin will be discussed. |
Sunday, November 24, 2024 11:20AM - 12:50PM |
C33.00022: INTERACT DISCUSSION SESSION WITH POSTERS: Aerodynamics from seeds to metamaterials 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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