2,172 research outputs found
Vortices and Forces in Biological Flight: Insects, Birds, and Bats
No full textInsects, 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 100 to 106. 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.</p
Lift of a bio-inspired flapping wing with a dynamic trailing-edge flap in forward flight
No full textUnlike the tail of a bird, regarded as a separately controlled aerodynamic surface, the membrane tail of a bat is operated as a dynamic trailing-edge flap. We investigate the effects of a dynamic trailing-edge flap on unsteady lift by numerically solving the Navier-Stokes equations around a bio-inspired flapping wing. The peak of the lift coefficient in the downstroke is considerably affected by the phase difference between the dynamic trailing-edge flap and the elevation. A quasi-steady formula is proposed to model the effects of phase difference on lift. The model is consistent with numerical results and experimental observations.</p
Yi-Nuo Wang, Piano
No full textYi-Nuo Wang, piano, performed Béla Bartók (1881-1945): Piano Sonata, Sz. 80; Johannes Brahms (1833-1897): 8 Klavierstücke, Op. 76; Chen Yi (b. 1953): Ba Ban; Sergei Rachmaninoff (1873-1943): Etude in D Minor, Op. 39, No. 8; Etude in D Major Op. 39, No. 9https://digitalcommons.rockefeller.edu/tri-institutional-noon-recitals/1003/thumbnail.jp
Hexacentrus expansus Wang & Shi 2005
No full text2.7 Hexacentrus expansus Wang & Shi, 2005 Hexacentrus expansus Wang & Shi, 2005; Guo et al., 2016 Material examined: 1 male, CHINA, Chongqing Prov., 16-vi-2019, coll. Wang Jun; 1 male, CHINA, Chongqing Prov., 16-vi-2019, coll. Wang Jun; 1 male, CHINA, Chongqing Prov., 16-vi-2019, coll. Wang Jun. Measurements (in mm): Male: SZ 44.39–45.21, PR 23.50–25.46, FW 36.19–36.77, HF 20.40–22.86.Published as part of Chen, Po-Wei, Xie, Hui-Cong, Wu, Xue, Shen, Chu-Ze & He, Zhu-Qing, 2021, A new species of genus Hexacentrus Serville, 1831 from Taiwan (Orthoptera Tettigoniidae: Hexacentrinae), pp. 543-556 in Zootaxa 4933 (4) on page 554, DOI: 10.11646/zootaxa.4933.4.5, http://zenodo.org/record/455669
Optimal reduced frequency for the power efficiency of a flat plate gliding with spanwise oscillations
No full textThe spanwise oscillation provides an accessory or alternative to flapping motion toward high-efficiency bio-inspired flight. The power factor that measures the efficiency of a gliding wing with spanwise oscillation to support a unit weight is investigated in this work. The gliding wing model consists of a rectangular flat plate that oscillates sinusoidally along the spanwise direction in a uniform upstream flow at a post-stall angle of attack. The unsteady flows and aerodynamic forces are obtained by numerically solving the incompressible Navier-Stokes equations at a Reynolds number of 300 (based on the uniform upstream velocity and the chord length). It is found that the spanwise oscillation can effectively enhance the power factor of the rectangular wing. The power factor under the optimal spanwise oscillation is 1.97 times as large as that without spanwise oscillation. Then, we introduce an effective reduced frequency by accounting for the effect of spanwise oscillation on the velocity encountered by the wing. The results show that the optimal effective reduced frequency locates in a narrow region from 0.47 to 0.56. Finally, the analyses of the vortex structures and the Lamb vector field indicate that the enhanced power factor results from the interaction between the stable leading-edge vortex and side-edge vortices associated with the spanwise oscillation. This work is expected to be helpful in understanding the vortex dynamics and guiding the kinematic design of the high-efficiency bio-inspired flight with spanwise oscillation
Simplified permeable surface correction for frequency-domain Ffowcs Williams and Hawkings integrals
No full textA simplified surface correction formulation is proposed to diminish the far-field spurious sound generated by the quadrupole source term in Ffowcs Williams and Hawkings (FW-H) integrals. The proposed formulation utilizes the far-field asymptotics of the Green's function to simplify the computation of its high-order derivatives, which circumvents the difficulties reported in the original frequency-domain surface correction formulation. The proposed formulation has been validated by investigating the benchmark case of sound generated by a convecting vortex. The results show that the proposed formulation successfully eliminates the spurious sound. The applications of the proposed formulation to flows with some special parameters are also discussed. (C) 2021 The Author(s). Published by Elsevier Ltd on behalf of The Chinese Society of Theoretical and Applied Mechanics
Orophyllus guttatus Xie, Wang & He 2021, sp. nov.
No full textOrophyllus guttatus Xie, Wang & He sp. nov. Figs. 5A–G Material examined: Holotype: 1 male, CHINA, Guangxi Prov., Maoershan (110.48°E, 25.88°N), 11-viii-2020 coll. Xie Hui-Cong (ECNU). Description. Male individuals are similar to Orophyllus supeciliarilamellatus sp. nov. (Figs. 5A–F), but differs in a dark spot at the base of the subgenital plate (Fig. 5G). Female unknown. Measurements (in mm): Male: SZ 42.51, PR 6.24, FW 34.43. Etymology: Species name guttatus means patches in the middle of subgenital and preceding plates. Distribution: Guangxi.Published as part of Xie, Hui-Cong, Wang, Han-Qiang, Li, Kai & He, Zhu-Qing, 2021, Taxonomy of genus Orophyllus Beier, 1954 (Orthoptera: Tettigoniidae: Pseudophyllinae), pp. 147-159 in Zootaxa 4990 (1) on page 154, DOI: 10.11646/zootaxa.4990.1.9, http://zenodo.org/record/498301
The motion of respiratory droplets produced by coughing
No full textCoronavirus disease 2019 has become a global pandemic infectious respiratory disease with high mortality and infectiousness. This paper investigates respiratory droplet transmission, which is critical to understanding, modeling, and controlling epidemics. In the present work, we implemented flow visualization, particle image velocimetry, and particle shadow tracking velocimetry to measure the velocity of the airflow and droplets involved in coughing and then constructed a physical model considering the evaporation effect to predict the motion of droplets under different weather conditions. The experimental results indicate that the convection velocity of cough airflow presents the relationship t(-0.7) with time; hence, the distance from the cougher increases by t(0.3) in the range of our measurement domain. Substituting these experimental results into the physical model reveals that small droplets (initial diameter D <= 100 mu m) evaporate to droplet nuclei and that large droplets with D >= 500 mu m and an initial velocity u(0) >= 5 m/s travel more than 2 m. Winter conditions of low temperature and high relative humidity can cause more droplets to settle to the ground, which may be a possible driver of a second pandemic wave in the autumn and winter seasons.</p
MS-based glycomic strategies for probing the structural details of polylactosaminoglycan chain on N-glycans and glycoproteomic identification of its protein carriers.
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