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 A27: Biological Fluid Dynamics: Flight |
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Chair: Geoffrey Spedding, USC Room: 609 |
Saturday, November 23, 2019 3:00PM - 3:13PM |
A27.00001: Unsteady aerodynamic characteristics of large scale bird flapping flight Zifeng Weng, Suyang Qin, Yang Xiang, Hong Liu Various unsteady aerodynamic mechanisms have been found in flapping flight especially at low Reynolds number (1E2-1E4). However, large scale bird flying at high Re (1E5) is mostly assumed to be quasi-steady. A two-jointed-wing robotic goose was built to carry out wind tunnel experiment. Force and PIV measurements were performed to study the unsteady force and flow field. Lift is found to change with average effective angle of attack and the average lift is close to that in cruising flight. Lift enhancement occurs in mid-downstroke, which is not induced by leading edge vortex but the result of enhacement of circulation. Thrust occurs in both upstroke and downstroke periods, and maximizes at mid-upstroke and mid-downstroke. Since flapping amplitude varies along wing span, thrust production is the overall result at different spanwise position. According to the flow field measurement, jet flow is found in the wake of handwing, but not in that of armwing. The phase difference between handwing and armwing results in larger flapping amplitude, i.e. higher St and thus enhances thrust production. In general, high Re flapping flight play its role mostly in propulsion, instead of producing high lift as that in low Re flight. And lift production might rely more on aerofoil and flow speed. [Preview Abstract] |
Saturday, November 23, 2019 3:13PM - 3:26PM |
A27.00002: Simulation of flapping bird flight, part 1: closed-loop control, forces, and wake topology Victor Colognesi, Gianmarco Ducci, Renaud Ronsse, Philippe Chatelain This work aims at reproducing bird flight in silico in order to shed light on its performance-enabling mechanisms. To that end, we establish an anatomical model of a bird with a pure flapping gait, the bald ibis. It combines a multibody model of the skeleton, with the corresponding joints and degrees of freedom, and a plumage model. The latter allows extracting the wing geometry and aerodynamic properties for any configuration of the skeleton. These properties are translated into a deforming immersed lifting line, which handles the sources of vorticity within a vortex particle-mesh method. The resulting multiphysics framework captures, at a high fidelity, the full flight dynamics, the required efforts and the resulting wake. A sensitivity analysis is carried out and leveraged for the design of a flight controller. Specifically, we quantity the influence of shoulder kinematic features on the aerodynamic forces and moments. The controller then uses these features as command parameters. This bird model can reach a trimmed state over various flight regimes and can handle transients between them. Finally, the accurate capture of the wake vortical structures allows their unambiguous identification and association with the time-varying aerodynamic forces produced by the bird. [Preview Abstract] |
Saturday, November 23, 2019 3:26PM - 3:39PM |
A27.00003: Simulation of flapping bird flight, part 2: Gait parametrization, limit cycle, and dynamic stability Gianmarco Ducci, Victor Colognesi, Philippe Chatelain, Renaud Ronsse We introduce a method to identify gait trajectories in trimmed flapping flight. Such trajectories correspond to limit cycles in the state space, characterized by the same period as the wingbeat. Our method relies on a multiple-shooting algorithm that can simultaneously identify unknown limit cycles, and analyze their stability. Based on Floquet theory, this analysis computes the Jacobian of the identified limit cycle and assesses its stability from its eigenvalues.\\ In a first contribution, we adapt this framework to the flapping flight equations of motion, known to be not only non-linear and time-dependent, but also driven by state-dependent forcing aerodynamic loads. An aerodynamic model was developed following the quasi-steady lifting line approach reported in part 1, taking the wing morphology and prescribed kinematics as input, and returning the state-dependent aerodynamic loads as output.\\ Our results identify one instable mode, suggesting that birds continuously rely on sensory feedback to achieve steady-state flapping flight. This framework is then leveraged in the analysis of several gait configurations. In particular, we use it to perform a sensitivity analysis of the flapping gaits required to achieve several flight regimes (level, climbing and descending flight). [Preview Abstract] |
Saturday, November 23, 2019 3:39PM - 3:52PM |
A27.00004: ABSTRACT WITHDRAWN |
Saturday, November 23, 2019 3:52PM - 4:05PM |
A27.00005: Holey wings can improve aerodynamics at bioscales Yohanna Hanna, Geoffrey Spedding The performance of wings at moderate Reynolds numbers ($10^4 \leq {\rm Re} \leq 10^5$) is strongly influenced by laminar boundary layer separation, and by the possible reattachment (in the mean sense) of the detached shear layer. Details of these events on both pressure and suction surfaces can lead to unexpected phenomena such as a negative lift slope around zero angle of attack, and abrupt changes in flow state close to the formation of a closed laminar separation bubble. Once understood, one may seek to exploit these sensitivities to find new forms of flow control, either passive or active. Here, we show that small, distributed porosity (porosity ratio, $\phi = 0.003$) on a wing at moderate Re can almost completely remove the nonlinearities in the $C_{\ell}(\alpha)$ curve, to yield a more robust and predictable lifting device. The flow-through mechanisms of a permeable wing are investigated and provide an alternative explanation for the sometimes-reported benefits in bio-flyers, that would then also apply to engineered equivalents of the same scale. [Preview Abstract] |
Saturday, November 23, 2019 4:05PM - 4:18PM |
A27.00006: Arrow flight and optimal feathers in archery Tom Maddalena, Caroline Cohen, Christophe Clanet In archery, athletes shoot arrows with their bow from 70 m on an outdoor field. The target is made of 10 concentric rings, from 12 cm to 1.20 m. Therefore, the angular tolerance of the smallest ring is 0.12/70 = 2 mrad. What is more, the environmental conditions such as wind or rain can have a huge impact on the arrow’s final position. Yet, a few centimeters on the target often distinguishes the winner from the others. All parameters of the bow and arrows must then be carefully selected in order to maximize the accuracy. In this work, we focus on the arrow’s flight, and more particularly on the choice of the optimal feathers. Archers can indeed choose among many size and shapes of feathers, and the effect of those feathers on the accuracy is still poorly understood. To tackle this question, we combine different experiments. We first shoot arrows with feathers of different size and shape with a throwing machine. Those experiments are eventually achieved with a lateral wind. We also characterize in a wind tunnel the influence of the feathers on the aerodynamic forces on the arrow. Those experiments combined with a theoretical model of the flight, allow to predict the trajectory of an arrow, and the influence of different perturbation on its final position. [Preview Abstract] |
Saturday, November 23, 2019 4:18PM - 4:31PM |
A27.00007: Falling of a plate with eccentric center of mass Sean Coughenour, Hui Wan The problem of a freely falling object is of interest in both fluid mechanics and nonlinear dynamics. Four types of motions have been observed, i.e., steady falling, flutter, tumble, and chaotic motion, depending on the body moment of inertia and the Reynolds number. For example, at high Reynolds number, flutter and tumble motion are obtained for bodies with small and large moment of inertia, respectively. Most of previous studies focused on the symmetric body with mass center collocated with the geometric center. In this study, we will numerically study the falling of a plate with eccentric center of mass. We will also adjust the center of the mass and thus change the moment of inertia and the~angular velocity of body rotation, therefore enabling a new methodology to actively control the plate falling trajectories. [Preview Abstract] |
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