Fig 6 - uploaded by Anders Hedenström
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A leading edge vortex attached to the wing midway through the downstroke of a Palla ’ s long-tongued bat Glossophaga soricina . (A) The blue patch in the top right corner is the start vortex shed at the beginning of the downstroke when lift is increasing rapidly. The black arrows show the induced velocity field, whereas red arrows along the wing chord show the velocity of a mid-wing segment. (B) Position along the wingspan of the measurement in A. Based on Muijres et al. (2008).
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Bats evolved the ability of powered flight more than 50 million years ago. The modern bat is an efficient flyer and recent research on bat flight has revealed many intriguing facts. By using particle image velocimetry to visualize wake vortices, both the magnitude and time-history of aerodynamic forces can be estimated. At most speeds the downstrok...
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... et al., 1996;Birch and Dickinson, 2001;Sane, 2003;Johansson et al., 2013), and a few bird species ( Muijres et al., 2012a, Warrick et al., 2009, Wolf et al., 2013. In this context, wind tunnel experiments of on-wing flow measurements of slow flying bats have demonstrated the presence of LEVs in the relatively small Palla's long-tongued bats ( Fig. 6; Muijres et al., 2008); in slow forward flight (1 m s −1 ) the LEV contributes up to 40% of the total aerodynamic force (Table 1). Thus far a LEV has been demonstrated also in another species, the lesser long-nosed bat (Table 1; Muijres et al., 2014), but there is nothing extraordinary about the morphology or flight style in these ...
Citations
... For example, convergent evolution at the genetic level is demonstrated by the striking similarities between the wing systems of birds and bats [40]. Despite having distinct evolutionary histories, bats and birds share wings that have separately developed to have comparable skeleton design and aerodynamic properties [41]. This convergence demonstrates how preexisting genetic toolkits can be used with natural selection to produce convergent outcomes [33]. ...
This tale explores the complex relationship between genetic creativity, adaptation and common ecological problems that is arranged by the master sculptor, natural selection. Convergence reveals the adaptive genius that runs throughout the structure of evolution and is an acknowledgment to the continued power of natural selection. This journey aims to solve the enigma of convergent evolution. Natural selection has been influencing every link in the complex web of life on Earth for more than a century. Understanding the carefully sculpted process of evolution and how life adapts to environmental difficulties was made possible by Charles Darwin's seminal research. Darwin postulated that the main force behind evolutionary advancement is natural selection. One of the remarkable effects of this process, which depends on individuals reproducing and surviving depending on heritable features, is convergence. The foundation of this fascinating subject is the well-balanced mechanism of natural selection, which promotes features an organism's chances of survival and reproduction. This is the tale of how natural selection drives convergence through adaptation, genetic innovation, and common ecological problems. In hostile environments like deserts and vast lengths of space, the great sculptor, natural selection, crafts living forms that converge on similar answers to common obstacles. The adaptive genius of convergent evolution demonstrates the continual influence of natural selection on the evolution of life. As we continue to solve the mysteries of convergent evolution, we are setting out on an adventure that will not only deepen our understanding of the past but also help us see the connections between seemingly unrelated species in the vast web of evolution and gain a deeper understanding of how interconnected all life is.
... Bat flight can be exceedingly complex in both natural and experimental conditions 63 , but the simulation model Flight 1.25 13 used can be applied to bats 13 to model steady, level, non-accelerating, forward flight, a baseline to establish whether the fossil Onychonycteris finneyi and modeled forms are capable of aerial locomotion using flapping with available muscle power. For this purpose, this aerodynamic model 13 renders acceptable power output in a range of forward airspeeds as compared to actual measures of kinematic energy contained in the wake of bats flying in a controlled setting 64 . ...
... We validated the aerodynamic model by comparing empirical parameters measured in both powered-flying bats and gliding mammals, with the Testing the model with the flight of extant bats is more complex as aerodynamic theory suggests that minimum power and, thus, preferred flight speed should increase with mass 21,63 . Bats can modify the shape of their wings 21 , and large bats can adopt higher lift coefficients or modify wingbeat frequency and angle of attack. ...
... A further sensitivity test on muscle mass was also carried out for powered flapping, initially testing the same range of mass estimates for Model 3 with the ascribed value of flight muscle of 8% of total body mass. A further test was carried out using a muscle mass of 10%, as used in the evaluation of flight in theropod dinosaurs 29 , although this is higher than the median value for extant bats 63 and very unlikely in Onychonycteris finneyi. Supplementary Table 6 shows that for all the body mass estimates with a muscle mass of 10% vertical lift (climb) was positive, however, airspeeds were greater than 6 ms −1 in normodense air. ...
The evolutionary transition to powered flight remains controversial in bats, the only flying mammals. We applied aerodynamic modeling to reconstruct flight in the oldest complete fossil bat, the archaic Onychonycteris finneyi from the early Eocene of North America. Results indicate that Onychonycteris was capable of both gliding and powered flight either in a standard normodense aerial medium or in the hyperdense atmosphere that we estimate for the Eocene from two independent palaeogeochemical proxies. Aerodynamic continuity across a morphological gradient is further demonstrated by modeled intermediate forms with increasing aspect ratio (AR) produced by digital elongation based on chiropteran developmental data. Here a gliding performance gradient emerged of decreasing sink rate with increasing AR that eventually allowed applying available muscle power to achieve level flight using flapping, which is greatly facilitated in hyperdense air. This gradient strongly supports a gliding (trees-down) transition to powered flight in bats.
... Similarly, Ref. [2] found that the wind-hairs had high sensitivity to reverse airflow to allow bats to monitor instabilities during slow flight that could lead to separation. It should also be noted that bats are incredibly complex fliers, and their wings contain many features that improve their performance [3]; therefore, they rely on such sensors to remain in full control during extreme manoeuvrability. It is not only bats that possess these sensing hairs; seals also use sensing whiskers [4], through which the oncoming flow direction and velocity can be felt according to the dynamic responses of their whiskers. ...
Bio-inspired flexible pillar-like wind-hairs show promise for the future of flying by feel by detecting critical flow events on an aerofoil during flight. To be able to characterise specific flow disturbances from the response of such sensors, quantitative PIV measurements of such flow-disturbance patterns were compared with sensor outputs under controlled conditions. Experiments were performed in a flow channel with an aerofoil equipped with a 2D array of such sensors when in uniform inflow conditions compared to when a well-defined gust was introduced upstream and was passing by. The gust was generated through the sudden deployment of a row of flaps on the suction side of a symmetric wing that was placed upstream of the aerofoil with the sensors. The resulting flow disturbance generated a starting vortex with two legs, which resembled a horseshoe-type vortex shed into the wake. Under the same tunnel conditions, PIV measurements were taken downstream of the gust generator to characterise the starting vortex, while further measurements were taken with the sensing pillars on the aerofoil in the same location. The disturbance pattern was compared to the pillar response to demonstrate the potential of flow-sensing pillars. It was found that the pillars could detect the arrival time and structural pattern of the flow disturbance, showing the characteristics of the induced flow field of the starting vortex when passing by. Therefore, such sensor arrays can detect the "footprint" of disturbances as temporal and spatial signatures, allowing us to distinguish those from others or noise.
... (a) Structure, layout, and dimensions of the simplified model wing; (b) schematic of the real bat wing, redrawn from the picture published by Hedenstrom and Johansson[26]. ...
Flapping-wing micro air vehicles (FWMAVs) have gained much attention from researchers due to their exceptional performance at low Reynolds numbers. However, the limited understanding of active aerodynamic modulation in flying creatures has hindered their maneuverability from reaching that of their biological counterparts. In this article, experimental investigations were conducted to examine the effect of the bilateral amplitude asymmetry of flexible flapping wings. A reduced bionic model featuring bat-like wings is built, and a dimensionless number ΔΦ* is introduced to scale the degree of bilateral amplitude asymmetry in flapping motion. The experimental results suggest that the bilateral amplitude–asymmetric flapping motion primarily induces maneuvering control forces of coupling roll moment and yaw moment. Also, roll moment and yaw moment have a good linear relationship. To achieve more efficient maneuvers based on this asymmetric motion, it is advisable to maintain ΔΦ* within the range of 0 to 0.4. The magnitude of passive pitching deformation during the downstroke is significantly greater than that during the upstroke. The phase of the peak of the passive pitching angle advances with the increase in flapping amplitude, while the valleys lag. And the proportion of pronation and supination in passive pitching motion cannot be adjusted by changing the flapping amplitude. These findings have important practical relevance for regulating turning maneuvers based on amplitude asymmetry and help to understand the active aerodynamic modulation mechanism through asymmetric wing kinematics.
... The span ratio of bat wings is approximately 0.6 at the lowest speed and 0.70-0.75 at medium and high speeds, which is higher than that for most birds (Norberg & Winter 2006, Tobalske 2007. For further details on bat wing morphology and kinematics, we refer the reader to Hedenström & Johansson (2015), Swartz & Konow (2015), Amador et al. (2020), and Sadier et al. (2020). ...
... The LEV is a convergent and robust mechanism normally observed in a large Re range (sizes) in the translation stroke of flapping wings (Figure 1) of insects (Ellington et al. 1996, Bomphrey et al. 2005, birds (Videler et al. 2004;Warrick et al. 2005Warrick et al. , 2012Hedenström et al. 2007Hedenström et al. , 2009Muir et al. 2017), and bats (Muijres et al. 2008, Hedenström & Johansson 2015 that prevents stall at high AoAs and augments lift production. The LEVs of flapping wings have been identified in experiments using dynamically scaled mechanical models (van den Berg & Ellington 1997, Lu et al. 2006, Lentink & Dickinson 2009, Phillips et al. 2015 and in CFD simulations (Liu et al. 1998, Sun & Wu 2003, Liu 2009, Liu & Aono 2009, Song et al. 2014) of various realistic and simplified models with flapping or revolving kinematic protocols (Kim & Gharib 2010, Ozen & Rockwell 2012, Garmann & Visbal 2014, Harbig et al. 2014, Carr et al. 2015, Wolfinger & Rockwell 2015. ...
Insects, birds, and bats that power and control flight by flapping their wings perform excellent flight stability and maneuverability by rapidly and continuously varying their wing motions. This article provides an overview of the state of the art of vortex-dominated, unsteady flapping aerodynamics from the viewpoint of diversity and uniformity associated with dominant vortices, particularly of the relevant physical aspects of the flight of insects and vertebrates in the low-and intermediate-Reynolds-number (Re) regime of 10 0 to 10 6. After briefly describing wing morphology and kinematics, we discuss the main vortices generated by flapping wings and the aerodynamic forces associated with these structures, focusing on leading-edge vortices (LEVs), wake vortices, and vortices generated by wing motions over a broad Re range. The LEVs are intensified by dynamic wing morphing in bird and bat flight, producing a significantly elevated vortex lift. The complex wake vortices are the footprints of lift generation; thus, the time-averaged vortex lift can be estimated from wake velocity data. Computational fluid dynamics modeling, quasi-steady models, and vortex lift models are useful tools to elucidate the intrinsic relationships between the lift and the dominant vortices in the near-and far-fields in flapping flight.
... As shown in Figure 1, the results of biological experiments on birds show that their necks comprise multiple sections in series, which have good rigidity and can effectively resist external disturbance, with each section implicating the next one by hinge and muscles. The skeletal muscles in each section act as an actuator, contracting when sensing the body shake to ensure the inertial stability of the head [35][36][37][38][39]. ...
... which have good rigidity and can effectively resist external disturbance, with each section implicating the next one by hinge and muscles. The skeletal muscles in each section act as an actuator, contracting when sensing the body shake to ensure the inertial stability of the head [35][36][37][38][39]. On the basis of the aforementioned biological research on bird necks, this paper proposes a bio-inspired space isolation unit. ...
The positioning accuracy of spacecraft in orbit is easily affected by low-frequency micro-vibrations of the environment and internal disturbances caused by the payload. Inspired by the neck structure of birds, this study devised a piezo-driven active vibration isolation unit with high stiffness. First, a dynamic model and two-sensor feedback control method for the isolation unit were developed, and the isolation mechanism and anti-disturbance characteristics were analyzed. Further, the stability of the closed-loop was verified. Simulation models of serial and parallel systems based on the proposed vibration isolation unit were implemented to demonstrate its feasibility. The results indicate that the proposed isolation units can provide excellent low-frequency vibration isolation performance and inertial stability and that they can effectively resist the internal disturbance of the payload. Moreover, its performance can be further improved via serial or parallel reconfiguration that facilitates its adaptation to the varied isolation requirements of spacecraft.
... The ratio of flight speed to power requirement is minimized at a speed somewhat greater than V mp , termed the maximum range speed (V mr ). In an ideal theoretical context, V mr is estimated at approximately 1.3 times V mp (Hedenström and Johansson, 2015). ...
... The span ratio of bat wings is approximately 0.6 at the lowest speed and 0.70-0.75 at medium and high speeds, which is higher than that for most birds (Norberg & Winter 2006, Tobalske 2007. For further details on bat wing morphology and kinematics, we refer the reader to Hedenström & Johansson (2015), Swartz & Konow (2015), Amador et al. (2020), and Sadier et al. (2020). ...
... The LEV is a convergent and robust mechanism normally observed in a large Re range (sizes) in the translation stroke of flapping wings (Figure 1) of insects (Ellington et al. 1996, Bomphrey et al. 2005, birds (Videler et al. 2004;Warrick et al. 2005Warrick et al. , 2012Hedenström et al. 2007Hedenström et al. , 2009Muir et al. 2017), and bats (Muijres et al. 2008, Hedenström & Johansson 2015 that prevents stall at high AoAs and augments lift production. The LEVs of flapping wings have been identified in experiments using dynamically scaled mechanical models (van den Berg & Ellington 1997, Lu et al. 2006, Lentink & Dickinson 2009, Phillips et al. 2015 and in CFD simulations (Liu et al. 1998, Sun & Wu 2003, Liu 2009, Liu & Aono 2009, Song et al. 2014) of various realistic and simplified models with flapping or revolving kinematic protocols (Kim & Gharib 2010, Ozen & Rockwell 2012, Garmann & Visbal 2014, Harbig et al. 2014, Carr et al. 2015, Wolfinger & Rockwell 2015. ...
Insects, birds, and bats that power and control flight by flapping their wings perform excellent flight stability and maneuverability by rapidly and continuously varying their wing motions. This article provides an overview of the state of the art of vortex-dominated, unsteady flapping aerodynamics from the viewpoint of diversity and uniformity associated with dominant vortices, particularly of the relevant physical aspects of the flight of insects and vertebrates in the low- and intermediate-Reynolds-number ( Re) regime of 10 ⁰ to 10 ⁶ . After briefly describing wing morphology and kinematics, we discuss the main vortices generated by flapping wings and the aerodynamic forces associated with these structures, focusing on leading-edge vortices (LEVs), wake vortices, and vortices generated by wing motions over a broad Re range. The LEVs are intensified by dynamic wing morphing in bird and bat flight, producing a significantly elevated vortex lift. The complex wake vortices are the footprints of lift generation; thus, the time-averaged vortex lift can be estimated from wake velocity data. Computational fluid dynamics modeling, quasi-steady models, and vortex lift models are useful tools to elucidate the intrinsic relationships between the lift and the dominant vortices in the near- and far-fields in flapping flight.
Expected final online publication date for the Annual Review of Fluid Mechanics, Volume 56 is January 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
... The flexible wings of natural fliers and swimmers with membrane components and appendages have lightweight structures, shape reconfigurable capability, and possibly perception ability to surrounding environments [5,6]. These favorable features enable the fliers/swimmers to adapt to complex environments with optimal performance and high maneuverability for locomotion purposes [7][8][9]. Given the superior aerodynamic performance of flexible wings, there has been an increasing interest to incorporate the aeroelastic effect of flexible wings into the nextgeneration intelligent and efficient morphing air vehicles. ...
... It is worth mentioning that the coefficients in Eq. (11) are similar to the coefficients determined from our numerical simulations in Eq. (9). ...
... The collected data can be used as the input of the scaling relations shown in Eqs. (9) and (30) to predict the aerodynamic forces for active control purposes. ...
We present a numerical study to characterize nonlinear unsteady aeroelastic interactions of two-dimensional flexible wings at high angles of attack. The coupled fluid–flexible wing system is solved by a body-fitted variational aeroelastic solver based on the fully coupled Navier–Stokes and nonlinear structural equations. Using the coupled fluid–structure analysis, this study is aimed to provide physical insight and correlations for the aeroelastic behavior of flexible wings in the parameter space of the angle of attack and the aeroelastic number. The phase diagrams of the aerodynamic performance are established to obtain the envelope curves of the optimal performance and determine the transition line of the drag variation. The effects of the angle of attack and the aeroelastic number on the aeroelastic behaviors are systematically examined. The time-averaged membrane deformation is positively correlated with a nondimensional number, the so-called Weber number. A new scaling relation is proposed based on the dynamic equilibrium between the aerodynamic force fluctuation and the combined inertia–elastic fluctuation. The unsteady aerodynamic force can be adjusted by manipulating the membrane vibration, the mass ratio, the Strouhal number, and the aeroelastic number. The numerical investigations provide design guidelines and have the potential to enhance the maneuverability and flight agility of micro air vehicles with flexible wing structures.
... Bats also adopt a strategy to obtain aerodynamic benefits by reducing the area and span of their wings in high-speed flight [34,35]. However, compared to birds, their change in wing area is limited. ...
This study focuses on the flapping mechanisms found in recently developed biometric flapping-wing air vehicles (FWAVs). FWAVs mimic the flight characteristics of flying animals, providing advantages such as maneuverability, inconspicuousness, and excellent flight efficiency in the low Reynolds number region. The flapping mechanism is a critical part of determining the aerodynamic performance of an FWAV since it is directly related to the wing motion. In this study, the flight characteristics of birds and bats are introduced, the incorporation of these flight characteristics into the development of FWAVs is elucidated, and the utilization of these flight characteristics in the development of FWAVs is explained. Next, the classification and analysis of flapping mechanisms are conducted based on wing motion and the strategy for improving aerodynamic performance. Lastly, the current research gap is elucidated, and potential future directions for further research are proposed. This review can serve as a guide during the early development stage of FWAVs.
