Effect of Hindwings on the Aerodynamics and Passive Dynamic Stability of a Hovering Hawkmoth.

Insects are able to fly stably in the complex environment of the various gusts that occur in nature. In addition, many insects suffer wing damage in their lives, but many species of insects are capable of flying without their hindwings. Here, we evaluated the effect of hindwings on aerodynamics using a Navier-Stokes-based numerical model, and then the passive dynamic stability was evaluated by coupling the equation of motion in three degrees of freedom with the aerodynamic forces estimated by the CFD solver under large and small perturbation conditions. In terms of aerodynamic effects, the presence of the hindwings slightly reduces the efficiency for lift generation but enhances the partial LEV circulation and increases the downwash around the wing root. In terms of thrust, increasing the wing area around the hindwing region increases the thrust, and the relationship is almost proportional at the cycle-averaged value. The passive dynamic stability was not clearly affected by the presence of the hindwings, but the stability was slightly improved depending on the perturbation direction. These results may be useful for the integrated design of wing geometry and flight control systems in the development of flapping-winged micro air vehicles.

Auditory sensory range of male mosquitoes for the detection of female flight sound.

Male mosquitoes detect and localize conspecific females by their flight-tones using the Johnston's organ (JO), which detects antennal deflections under the influence of local particle motion. Acoustic behaviours of mosquitoes and their JO physiology have been investigated extensively within the frequency domain, yet the auditory sensory range and the behaviour of males at the initiation of phonotactic flights are not well known. In this study, we predict a maximum spatial sensory envelope for flying Culex quinquefasciatus by integrating the physiological tuning response of the male JO with female aeroacoustic signatures derived from numerical simulations. Our sensory envelope predictions were tested with a behavioural assay of free-flying males responding to a female-like artificial pure tone. The minimum detectable particle velocity observed during flight tests was in good agreement with our theoretical prediction formed by the peak JO sensitivity measured in previous studies. The iso-surface describing the minimal detectable particle velocity represents the quantitative auditory sensory range of males and is directional with respect to the female body orientation. Our results illuminate the intricacy of the mating behaviour and point to the importance of observing the body orientation of flying mosquitoes to understand fully the sensory ecology of conspecific communication.

Compact Sphere-Shaped Airflow Vector Sensor Based on MEMS Differential Pressure Sensors.

This paper presents an airflow vector sensor for drones. Drones are expected to play a role in various industrial fields. However, the further improvement of flight stability is a significant issue. In particular, compact drones are more affected by wind during flight. Thus, it is desirable to detect air current directly by an airflow sensor and feedback to the control. In the case of a drone in flight, the sensor should detect wind velocity and direction, particularly in the horizontal direction, for a sudden crosswind. In addition, the sensor must also be small, light, and highly sensitive. Here, we propose a compact spherical airflow sensor for drones. Three highly sensitive microelectromechanical system (MEMS) differential pressure (DP) sensor chips were built in the spherical housing as the sensor elements. The 2D wind direction and velocity can be measured from these sensor elements. The fabricated airflow sensor was attached to a small toy drone. It was demonstrated that the sensor provided an output corresponding to the wind velocity and direction when horizontal wind was applied via a fan while the drone was flying. The experimental results demonstrate that the proposed sensor will be helpful for directly measuring the air current for a drone in flight.

Improvement of abnormal cervical cytology possibly due to a graft-versus-tumor effect: A case report and literature review.

The cervical cytology of our patient transformed from squamous cell carcinoma to negative for intraepithelial lesion or malignancy, possibly due to the graft-versus-tumor effect following allogeneic stem cell transplantation.

Aeroacoustic characteristics of owl-inspired blade designs in a mixed flow fan: effects of leading- and trailing-edge serrations.

There is an increasing need in industry for noise reduction in fans. Inspired by owls' silent flight, we propose four owl-inspired blade designs for a mixed-flow fan to examine whether leading-edge (LE) and/or trailing-edge (TE) serrations can resolve the tradeoff between sound suppression and aerodynamic performance. We investigate the blades' aeroacoustic characteristics through various experimental methods and large-eddy simulation (LES)-based numerical analyses. Experimental results suggest that 'slotted', simply-fabricated LE serrations can achieve a lowering of the noise level while sustaining the aerodynamic performance of the fan, whereas TE serrations fail. In addition, the inclination angle can improve LE serration performance in aeroacoustic and aerodynamic performance with a reduction in the specific noise level by around 1.4 dB. LES results and noise spectral analysis indicate that the LE serrations can suppress flow separation, reducing the broadband noise at low-to-middle frequencies (40-4k Hz). This passive-flow-control mechanism, likely due to local higher incidence angles associated with LE serrations, is capable of alleviating the intensive pressure gradient while suppressing wall-pressure fluctuations over the LE region, hence weakening the Kelvin-Helmholtz instability. The tonal noise also shows a marked reduction at the highest peak frequency associated with fan-vane interaction. Moreover, we find that the high-frequency noise by-product radiates mainly from the LE serrations andsurroundings, due to the small eddies broken up when the vortical flows pass through the LE serrations. Our results demonstrate that the biomimetic design of the LE serrations can facilitate the break-up of LE vortices passively and effectively without negatively impacting aerodynamic performance, which can be utilized as an effective device to improve the aeroacoustic performance of fan blades.

Flexible Flaps Inspired by Avian Feathers Can Enhance Aerodynamic Robustness in low Reynolds Number Airfoils.

Unlike rigid rotors of drones, bird wings are composed of flexible feathers that can passively deform while achieving remarkable aerodynamic robustness in response to wind gusts. In this study, we conduct an experimental study on the effects of the flexible flaps inspired by the covert of bird wings on aerodynamic characteristics of fixed-wings in disturbances. Through force measurements and flow visualization in a low-speed wind tunnel, it is found that the flexible flaps can suppress the large-scale vortex shedding and hence reduce the fluctuations of aerodynamic forces in a disturbed flow behind an oscillating plate. Our results demonstrate that the stiffness of the flaps strongly affects the aerodynamic performance, and the force fluctuations are observed to be reduced when the deformation synchronizes with the strong vortex generation. The results point out that the simple attachment of the flexible flaps on the upper surface of the wing is an effective method, providing a novel biomimetic design to improve the aerodynamic robustness of small-scale drones with fixed-wings operating in unpredictable aerial environments.

Flexibility Effects of a Flapping Mechanism Inspired by Insect Musculoskeletal System on Flight Performance.

Flying animals such as insects display great flight performances with high stability and maneuverability even under unpredictable disturbances in natural and man-made environments. Unlike man-made mechanical systems like a drone, insects can achieve various flapping motions through their flexible musculoskeletal systems. However, it remains poorly understood whether flexibility affects flight performances or not. Here, we conducted an experimental study on the effects of the flexibility associated with the flapping mechanisms on aerodynamic performance with a flexible flapping mechanism (FFM) inspired by the flexible musculoskeletal system of insects. Based on wing kinematic and force measurements, we found an appropriate combination of the flexible components could improve the aerodynamic efficiency by increasing the wingbeat amplitude. Results of the wind tunnel experiments suggested that, through some passive adjustment of the wing kinematics in concert with the flexible mechanism, the disturbance-induced effects could be suppressed. Therefore, the flight stability under the disturbances is improved. While the FFM with the most rigid spring was least efficient in the static experiments, the model was most robust against the wind within the range of the study. Our results, particularly regarding the trade-off between the efficiency and the robustness, point out the importance of the passive response of the flapping mechanisms, which may provide a functional biomimetic design for the flapping micro air vehicles (MAVs) capable of achieving high efficiency and stability.

Intermittent control strategy can enhance stabilization robustness in bumblebee hovering.

Active flight control plays a crucial role in stabilizing the body posture of insects to stay aloft under a complex natural environment. Insects can achieve a closed-loop flight control by integrating the external mechanical system and the internal working system through manipulating wing kinematics according to feedback information from multiple sensors. While studies of proportional derivative/proportional integral derivative-based algorithms are the main subject to explore the continuous flight control mechanisms associated with insect flights, it is normally observed that insects achieve an intermittent spike firing in steering muscles to manipulate wings in flight control discontinuously. Here we proposed a novel intermittent control strategy for a 3 degree of freedom (DoF) pitch-control and explored its stabilization robustness in bumblebee hovering. An integrated computational model was established and validated, which comprises an insect-inspired dynamic flight simulator and a novel discrete feedback controller as well as a simplified free-flight dynamic model. We found that the intermittent control model can achieve an angular-dominant flight control, whereas the continuous control model corresponds to an angular-velocity-dominant one. Given the biological constraints in sensorimotor neurobiology and musculoskeletal mechanics, the intermittent control strategy was examined capable of enhancing the stabilization robustness in terms of sensory latency, stroke derivation, spike interval, and damping strength. Our results indicate that the intermittent control strategy is likely a sophisticated flight control mechanism in insect flights while providing a bioinspired flight-control design for insect size flapping-wing micro air vehicles.

Aerodynamic imaging by mosquitoes inspires a surface detector for autonomous flying vehicles.

Some flying animals use active sensing to perceive and avoid obstacles. Nocturnal mosquitoes exhibit a behavioral response to divert away from surfaces when vision is unavailable, indicating a short-range, mechanosensory collision-avoidance mechanism. We suggest that this behavior is mediated by perceiving modulations of their self-induced airflow patterns as they enter a ground or wall effect. We used computational fluid dynamics simulations of low-altitude and near-wall flights based on in vivo high-speed kinematic measurements to quantify changes in the self-generated pressure and velocity cues at the sensitive mechanosensory antennae. We validated the principle that encoding aerodynamic information can enable collision avoidance by developing a quadcopter with a sensory system inspired by the mosquito. Such low-power sensing systems have major potential for future use in safer rotorcraft control systems.

Development of Mixed Flow Fans with Bio-Inspired Grooves.

Mixed flow fan is a kind of widely used turbomachine, which has faced problems of further performance improvement in traditional design methods in recent decades. Inspired by the microgrooves such as riblets and denticles on bird feathers and shark skins, we here propose biomimetic designs of various blades with the bio-inspired grooves, aiming at the improvement of the aeroacoustic performance. Based on a systematic study with computational fluid dynamic analyses, we found that these designs had the potential in noise suppression even with macroscopic grooves. Our best design can suppress turbulence kinetic energy by approximately 38% at the blade leading edge with aerodynamic efficiency loss of only 0.3 percentage points. This improvement is achieved by passive flow control. The vortical structures are changed in a favorable way at the leading edge due to the grooves. We believe that these biomimetic designs could provide a promising future of enhancing the performance of mixed flow fans by making grooves of ideal flow passages on the suction faces of blades in accord with the theory of pump design.

Forewings match the formation of leading-edge vortices and dominate aerodynamic force production in revolving insect wings.

In many flying insects, forewings and hindwings are coupled mechanically to achieve flapping flight synchronously while being driven by action of the forewings. How the forewings and hindwings as well as their morphologies contribute to aerodynamic force production and flight control remains unclear. Here we address the point that the forewings can produce most of the aerodynamic forces even with the hindwings removed through a computational fluid dynamic study of three revolving insect wing models, which are identical to the wing morphologies and Reynolds numbers of hawkmoth (Manduca sexta), bumblebee (Bombus ignitus) and fruitfly (Drosophila melanogaster). We find that the forewing morphologies match the formation of leading-edge vortices (LEV) and are responsible for generating sufficient lift forces at the mean angles of attack and the Reynolds numbers where the three representative insects fly. The LEV formation and pressure loading keep almost unchanged with the hindwing removed, and even lead to some improvement in power factor and aerodynamic efficiency. Moreover, our results indicate that the size and strength of the LEVs can be well quantified with introduction of a conical LEV angle, which varies remarkably with angles of attack and Reynolds numbers but within the forewing region while showing less sensitivity to the wing morphologies. This implies that the forewing morphology very likely plays a dominant role in achieving low-Reynolds number aerodynamic performance in natural flyers as well as in revolving and/or flapping micro air vehicles.

Quantifying the dynamic wing morphing of hovering hummingbird.

Animal wings are lightweight and flexible; hence, during flapping flight their shapes change. It has been known that such dynamic wing morphing reduces aerodynamic cost in insects, but the consequences in vertebrate flyers, particularly birds, are not well understood. We have developed a method to reconstruct a three-dimensional wing model of a bird from the wing outline and the feather shafts (rachides). The morphological and kinematic parameters can be obtained using the wing model, and the numerical or mechanical simulations may also be carried out. To test the effectiveness of the method, we recorded the hovering flight of a hummingbird (Amazilia amazilia) using high-speed cameras and reconstructed the right wing. The wing shape varied substantially within a stroke cycle. Specifically, the maximum and minimum wing areas differed by 18%, presumably due to feather sliding; the wing was bent near the wrist joint, towards the upward direction and opposite to the stroke direction; positive upward camber and the 'washout' twist (monotonic decrease in the angle of incidence from the proximal to distal wing) were observed during both half-strokes; the spanwise distribution of the twist was uniform during downstroke, but an abrupt increase near the wrist joint was found during upstroke.

Owl-inspired leading-edge serrations play a crucial role in aerodynamic force production and sound suppression.

Owls are widely known for silent flight, achieving remarkably low noise gliding and flapping flights owing to their unique wing morphologies, which are normally characterized by leading-edge serrations, trailing-edge fringes and velvet-like surfaces. How these morphological features affect aerodynamic force production and sound suppression or noise reduction, however, is still not well known. Here we address an integrated study of owl-inspired single feather wing models with and without leading-edge serrations by combining large-eddy simulations (LES) with particle-image velocimetry (PIV) and force measurements in a low-speed wind tunnel. With velocity and pressure spectra analysis, we demonstrate that leading-edge serrations can passively control the laminar-turbulent transition over the upper wing surface, i.e. the suction surface at all angles of attack (0° < AoA < 20°), and hence play a crucial role in aerodynamic force and sound production. We find that there exists a tradeoff between force production and sound suppression: serrated leading-edges reduce aerodynamic performance at lower AoAs < 15° compared to clean leading-edges but are capable of achieving both noise reduction and aerodynamic performance at higher AoAs > 15° where owl wings often reach in flight. Our results indicate that the owl-inspired leading-edge serrations may be a useful device for aero-acoustic control in biomimetic rotor designs for wind turbines, aircrafts, multi-rotor drones as well as other fluid machinery.

Smart wing rotation and trailing-edge vortices enable high frequency mosquito flight.

Mosquitoes exhibit unusual wing kinematics; their long, slender wings flap at remarkably high frequencies for their size (>800 Hz)and with lower stroke amplitudes than any other insect group. This shifts weight support away from the translation-dominated, aerodynamic mechanisms used by most insects, as well as by helicopters and aeroplanes, towards poorly understood rotational mechanisms that occur when pitching at the end of each half-stroke. Here we report free-flight mosquito wing kinematics, solve the full Navier-Stokes equations using computational fluid dynamics with overset grids, and validate our results with in vivo flow measurements. We show that, although mosquitoes use familiar separated flow patterns, much of the aerodynamic force that supports their weight is generated in a manner unlike any previously described for a flying animal. There are three key features: leading-edge vortices (a well-known mechanism that appears to be almost ubiquitous in insect flight), trailing-edge vortices caused by a form of wake capture at stroke reversal, and rotational drag. The two new elements are largely independent of the wing velocity, instead relying on rapid changes in the pitch angle (wing rotation) at the end of each half-stroke, and they are therefore relatively immune to the shallow flapping amplitude. Moreover, these mechanisms are particularly well suited to high aspect ratio mosquito wings.

Flight of the dragonflies and damselflies.

This work is a synthesis of our current understanding of the mechanics, aerodynamics and visually mediated control of dragonfly and damselfly flight, with the addition of new experimental and computational data in several key areas. These are: the diversity of dragonfly wing morphologies, the aerodynamics of gliding flight, force generation in flapping flight, aerodynamic efficiency, comparative flight performance and pursuit strategies during predatory and territorial flights. New data are set in context by brief reviews covering anatomy at several scales, insect aerodynamics, neuromechanics and behaviour. We achieve a new perspective by means of a diverse range of techniques, including laser-line mapping of wing topographies, computational fluid dynamics simulations of finely detailed wing geometries, quantitative imaging using particle image velocimetry of on-wing and wake flow patterns, classical aerodynamic theory, photography in the field, infrared motion capture and multi-camera optical tracking of free flight trajectories in laboratory environments. Our comprehensive approach enables a novel synthesis of datasets and subfields that integrates many aspects of flight from the neurobiology of the compound eye, through the aeromechanical interface with the surrounding fluid, to flight performance under cruising and higher-energy behavioural modes.This article is part of the themed issue 'Moving in a moving medium: new perspectives on flight'.

Enhanced flight performance by genetic manipulation of wing shape in Drosophila.

Insect wing shapes are remarkably diverse and the combination of shape and kinematics determines both aerial capabilities and power requirements. However, the contribution of any specific morphological feature to performance is not known. Using targeted RNA interference to modify wing shape far beyond the natural variation found within the population of a single species, we show a direct effect on flight performance that can be explained by physical modelling of the novel wing geometry. Our data show that altering the expression of a single gene can significantly enhance aerial agility and that the Drosophila wing shape is not, therefore, optimized for certain flight performance characteristics that are known to be important. Our technique points in a new direction for experiments on the evolution of performance specialities in animals.

The complex aerodynamic footprint of desert locusts revealed by large-volume tomographic particle image velocimetry.

Particle image velocimetry has been the preferred experimental technique with which to study the aerodynamics of animal flight for over a decade. In that time, hardware has become more accessible and the software has progressed from the acquisition of planes through the flow field to the reconstruction of small volumetric measurements. Until now, it has not been possible to capture large volumes that incorporate the full wavelength of the aerodynamic track left behind during a complete wingbeat cycle. Here, we use a unique apparatus to acquire the first instantaneous wake volume of a flying animal's entire wingbeat. We confirm the presence of wake deformation behind desert locusts and quantify the effect of that deformation on estimates of aerodynamic force and the efficiency of lift generation. We present previously undescribed vortex wake phenomena, including entrainment around the wing-tip vortices of a set of secondary vortices borne of Kelvin-Helmholtz instability in the shear layer behind the flapping wings.

A CFD-informed quasi-steady model of flapping wing aerodynamics.

Aerodynamic performance and agility during flapping flight are determined by the combination of wing shape and kinematics. The degree of morphological and kinematic optimisation is unknown and depends upon a large parameter space. Aimed at providing an accurate and computationally inexpensive modelling tool for flapping-wing aerodynamics, we propose a novel CFD (computational fluid dynamics)-informed quasi-steady model (CIQSM), which assumes that the aerodynamic forces on a flapping wing can be decomposed into the quasi-steady forces and parameterised based on CFD results. Using least-squares fitting, we determine a set of proportional coefficients for the quasi-steady model relating wing kinematics to instantaneous aerodynamic force and torque; we calculate power with the product of quasi-steady torques and angular velocity. With the quasi-steady model fully and independently parameterised on the basis of high-fidelity CFD modelling, it is capable of predicting flapping-wing aerodynamic forces and power more accurately than the conventional blade element model (BEM) does. The improvement can be attributed to, for instance, taking into account the effects of the induced downwash and the wing tip vortex on the force generation and power consumption. Our model is validated by comparing the aerodynamics of a CFD model and the present quasi-steady model using the example case of a hovering hawkmoth. It demonstrates that the CIQSM outperforms the conventional BEM while remaining computationally cheap, and hence can be an effective tool for revealing the mechanisms of optimization and control of kinematics and morphology in flapping-wing flight for both bio-flyers and unmanned air systems.

Aerodynamic performance of a hovering hawkmoth with flexible wings: a computational approach.

Insect wings are deformable structures that change shape passively and dynamically owing to inertial and aerodynamic forces during flight. It is still unclear how the three-dimensional and passive change of wing kinematics owing to inherent wing flexibility contributes to unsteady aerodynamics and energetics in insect flapping flight. Here, we perform a systematic fluid-structure interaction based analysis on the aerodynamic performance of a hovering hawkmoth, Manduca, with an integrated computational model of a hovering insect with rigid and flexible wings. Aerodynamic performance of flapping wings with passive deformation or prescribed deformation is evaluated in terms of aerodynamic force, power and efficiency. Our results reveal that wing flexibility can increase downwash in wake and hence aerodynamic force: first, a dynamic wing bending is observed, which delays the breakdown of leading edge vortex near the wing tip, responsible for augmenting the aerodynamic force-production; second, a combination of the dynamic change of wing bending and twist favourably modifies the wing kinematics in the distal area, which leads to the aerodynamic force enhancement immediately before stroke reversal. Moreover, an increase in hovering efficiency of the flexible wing is achieved as a result of the wing twist. An extensive study of wing stiffness effect on aerodynamic performance is further conducted through a tuning of Young's modulus and thickness, indicating that insect wing structures may be optimized not only in terms of aerodynamic performance but also dependent on many factors, such as the wing strength, the circulation capability of wing veins and the control of wing movements.

Regio- and stereoselective oxidation of propranolol enantiomers by human CYP2D6, cynomolgus monkey CYP2D17 and marmoset CYP2D19.

Toxic and pharmacokinetic profiles of drug candidates are evaluated in vivo often using monkeys as experimental animals, and the data obtained are extrapolated to humans. Well understanding physiological properties, including drug-metabolizing enzymes, of monkeys should increase the accuracy of the extrapolation. The present study was performed to compare regio- and stereoselectivity in the oxidation of propranolol (PL), a chiral substrate, by cytochrome P450 2D (CYP2D) enzymes among humans, cynomolgus monkeys and marmosets. Complimentary DNAs encoding human CYP2D6, cynomolgus monkey CYP2D17 and marmoset CYP2D19 were cloned, and their proteins expressed in a yeast cell expression system. The regio- and stereoselective oxidation of PL enantiomers by yeast cell microsomal fractions were compared. In terms of efficiency of expression in the system, the holo-proteins ranked CYP2D6=CYP2D17>>CYP2D19. This may be caused by the bulky side chain of the amino acid residue at position 119 (leucine for CYP2D19 vs. valine for CYP2D6 and CYP2D17), which can disturb the incorporation of the heme moiety into the active-site cavity. PL enantiomers were oxidized by all of the enzymes mainly into 4-hydroxyproranolol (4-OH-PL), followed by 5-OH-PL and N-desisopropylpropranolol (NDP). In the kinetic analysis, apparent K(m) values were commonly in the µM range and substrate enantioselectivity of R-PL