This study experimentally investigates aerodynamic characteristics and flow fields of a smooth owl-like airfoil without serrations and velvet structures. This biologically inspired airfoil design is intended to serve ...This study experimentally investigates aerodynamic characteristics and flow fields of a smooth owl-like airfoil without serrations and velvet structures. This biologically inspired airfoil design is intended to serve as the main-wing for low-Reynolds-number aircrafts such as micro air vehicles. Reynolds number dependency on aerodynamics is also evaluated at low Reynolds numbers. The results of the study show that the owl-like airfoil has high lift performance with a nonlinear lift increase due to the presence of a separation bubble on the suction side. A distinctive flow feature of the owl airfoil is a separation bubble on the pressure side at low angles of attack. The separation bubble switches location from the pressure side to the suction side as the angle of attack increases and is continuously present on the surface within a wide range of angles of attack. The Reynolds number dependency on the lift curves is insignificant, although differences in the drag curves are especially pronounced at high angles of attack. Eventually, we obtain the geometric feature of the owl-like airfoil to increase aerodynamic performance at low Reynolds numbers.展开更多
The loss of biodiversity from urbanized areas is a major environmental problem challenging policy-makers throughout the world.Solutions to this problem are urgently required in China.We carried out a case study of win...The loss of biodiversity from urbanized areas is a major environmental problem challenging policy-makers throughout the world.Solutions to this problem are urgently required in China.We carried out a case study of wintering long-eared owls(Asio otus)and their main prey to illustrate the negative effects of urbanization combined with ineffective conservation of biodiversity in Beijing.Field monitoring of owl numbers at two roosting sites from 2004 to 2012 showed that the owl population had fallen rapidly in metropolitan Beijing.Analysis of pellet contents identified only seven individuals of two species of shrew.The majority of mammalian prey comprised four bat and seven rodent species,making up 29.3%and 29.5%of the prey items,respectively.Prey composition varied significantly among years at the two sample sites.At the urban site the consumption of bats and rodents declined gradually over time,while predation on birds increased.In contrast,at the suburban site the prey composition showed an overall decrease in the number of bats,a sharp increase and a subsequent decrease in bird prey,and the number of rodent prey fell to a low point.Rapid development of real estate and inadequate greenfield management in city parks resulted in negative effects on the bird and small mammal habitat of urban areas in Beijing.We suggest that measures to conserve biodiversity should be integrated into future urban planning to maintain China’s rich biodiversity while also achieving sustainable economic development.展开更多
Many species of owls are able to fly noiselessly, and their wing feathers play an important role for the silent flight. In this paper, we studied the sound suppression mechanism of the eagle owl （Bubo bubo） by Stere...Many species of owls are able to fly noiselessly, and their wing feathers play an important role for the silent flight. In this paper, we studied the sound suppression mechanism of the eagle owl （Bubo bubo） by Stereo Microscope （SM）, Scanning Electron Microscopy （SEM） and Laser Scanning Confocal Microscope （LSCM）. To investigate the effects of special charac- teristics of wing feather on owl silent flight, the acoustic properties, including the sound absorption coefficient and flight noise, were compared between the eagle owl and common buzzard （Buteo buteo）. The results show that the eagle owl generates lower noise than common buzzard during flight, and its wing feather has better sound absorption properties. The leading edge serration and trailing edge fringe can improve the pressure fluctuation of turbulence boundary, and suppress the generation of vortex sound. The elongated distal barbules form a multi-layer grid porous structure which also has an effect on sound absorption. This research not only can give the inspiration for solving the aerodynamic noise of aircraft and engineering machine, but also can provide a new idea for the design of low-noise devices.展开更多
High-resolution Particle-Image Velocimetry （PIV） and time-resolved force measurements were performed to analyze the impact of the comb-like structure on the leading edge of barn owl wings on the flow field and overa...High-resolution Particle-Image Velocimetry （PIV） and time-resolved force measurements were performed to analyze the impact of the comb-like structure on the leading edge of barn owl wings on the flow field and overall aerodynamic performance. The Reynolds number was varied in the range of 40,000 to 120,000 and the range of angle of attack was 0° to 6° for the PIV and -15° to ＋20° for the force measurements to cover the full flight envelope of the owl. As a reference, a wind-tunnel model which possessed a geometry based on the shape of a typical barn owl wing without any owl-specific adaptations was built, and measurements were performed in the aforementioned Reynolds number and angle of attack： range. This clean wing model shows a separation bubble in the distal part of the wing at higher angles of attack. Two types of comb-like structures, i.e., artificial serrations, were manufactured to model the owl＇s leading edge with respect to its length, thickness, and material properties. The artificial structures were able to reduce the size of the separation region and additionally cause a more uniform size of the vortical structures shed by the separation bubble within the Reynolds number range investigated, resulting in stable gliding flight independent of the flight velocity. However, due to increased drag coefficients in conjunction with similar lift coefficients, the overall aerodynamic performance, i.e., lift-to-drag ratio is reduced for the serrated models. Nevertheless, especially at lower Reynolds numbers the stabilizing effect of the uniform vortex size outperforms the lower aerodynamic performance.展开更多
采用大涡模拟技术对长耳鸮翅膀展向20%、40%和60%截面处翼型的非定常湍流场进行数值模拟,并基于Lighthill声类比方法对非定常流场诱导的声场进行计算,研究上述仿生翼型的气动与声学性能。研究结果表明:三种仿生翼型均具有高升阻比特性,...采用大涡模拟技术对长耳鸮翅膀展向20%、40%和60%截面处翼型的非定常湍流场进行数值模拟,并基于Lighthill声类比方法对非定常流场诱导的声场进行计算,研究上述仿生翼型的气动与声学性能。研究结果表明:三种仿生翼型均具有高升阻比特性,其中20%、40%截面处翼型的升力系数较高,5°攻角下分别为1.86和1.72;20%截面处翼型阻力系数最高,且在强烈的逆压梯度下,20%和40%截面处翼型气流在压力面前缘开始分离,在下游处自由剪切层产生了明显的不规则涡结构;翼型尾缘处,涡流脱落后在尾迹区发生涡结构破碎;60%截面处翼型载荷分布最均匀,附面层增长缓慢,因而该翼型流场的涡量相对较小,使得其诱导噪声较低。声学计算结果表明,三种仿生翼型的最大声压级分别为85.8、78.6和74.8 d B。展开更多
Flow control can effectively reduce the aerodynamic noise radiated from a circular cylinder. As one of the flow control methods, a bionic method, inspired by the serrations at the leading edge of owls＇ wing, was prop...Flow control can effectively reduce the aerodynamic noise radiated from a circular cylinder. As one of the flow control methods, a bionic method, inspired by the serrations at the leading edge of owls＇ wing, was proposed in this paper. The effects of bionic serrated structures arranged on the upper and lower sides of a cylinder on the aerodynamic and aeroacoustic performance of the cylinder were numerically investigated. At a free stream speed of 24.5 m.s-1, corresponding to Reynolds number of 1.58 × 10^4, the simulation results indicate that the bionic serrated structures can decrease the frequency of the vortex shedding and control the fluctuating aerodynamic force acting on the cylinder, thus reduce the aerodynamic noise. A qualitative view of the vorticity in the wake of the cylinder suggest that the serrated structures reduce aerodynamic sound by suppressing the unsteady motion of vortices.展开更多
文摘This study experimentally investigates aerodynamic characteristics and flow fields of a smooth owl-like airfoil without serrations and velvet structures. This biologically inspired airfoil design is intended to serve as the main-wing for low-Reynolds-number aircrafts such as micro air vehicles. Reynolds number dependency on aerodynamics is also evaluated at low Reynolds numbers. The results of the study show that the owl-like airfoil has high lift performance with a nonlinear lift increase due to the presence of a separation bubble on the suction side. A distinctive flow feature of the owl airfoil is a separation bubble on the pressure side at low angles of attack. The separation bubble switches location from the pressure side to the suction side as the angle of attack increases and is continuously present on the surface within a wide range of angles of attack. The Reynolds number dependency on the lift curves is insignificant, although differences in the drag curves are especially pronounced at high angles of attack. Eventually, we obtain the geometric feature of the owl-like airfoil to increase aerodynamic performance at low Reynolds numbers.
基金This work was funded by the National Science Foundation of China for National Biological Science Base(J1103516).We thank the following postgraduate students from our research group for collecting and analyzing owl pellets throughout the years of this study:BM Peng,LJ Zhang,XJ Li,L Yuan,AM Wang and PL Yu.We appreciate helpful comments and English proofreading of the manuscript by Y.Wang.of the Alabama Agriculture and Machinery University.We declare that all sources of funding have been acknowledged and that there are no conflicts of interest regarding financial support.
文摘The loss of biodiversity from urbanized areas is a major environmental problem challenging policy-makers throughout the world.Solutions to this problem are urgently required in China.We carried out a case study of wintering long-eared owls(Asio otus)and their main prey to illustrate the negative effects of urbanization combined with ineffective conservation of biodiversity in Beijing.Field monitoring of owl numbers at two roosting sites from 2004 to 2012 showed that the owl population had fallen rapidly in metropolitan Beijing.Analysis of pellet contents identified only seven individuals of two species of shrew.The majority of mammalian prey comprised four bat and seven rodent species,making up 29.3%and 29.5%of the prey items,respectively.Prey composition varied significantly among years at the two sample sites.At the urban site the consumption of bats and rodents declined gradually over time,while predation on birds increased.In contrast,at the suburban site the prey composition showed an overall decrease in the number of bats,a sharp increase and a subsequent decrease in bird prey,and the number of rodent prey fell to a low point.Rapid development of real estate and inadequate greenfield management in city parks resulted in negative effects on the bird and small mammal habitat of urban areas in Beijing.We suggest that measures to conserve biodiversity should be integrated into future urban planning to maintain China’s rich biodiversity while also achieving sustainable economic development.
基金Acknowledgments This work is supported by the Special Funds of National Natural Science Foundation of China （Grant No. 31071928）, the International Cooperation Project of National Natural Science Foundation of China （Grant No. 50920105504）, the Science Development Foundation of Jilin Province （Grant No. 20090340）, the Basic Research of High-speed Rail Joint Funds of the National Natural Science Foundation of China （Grant No. Ul134109）, and the Specialized Research Fund for the Doctoral Program of Higher Education of China （Grant No. 20110061120048）
文摘Many species of owls are able to fly noiselessly, and their wing feathers play an important role for the silent flight. In this paper, we studied the sound suppression mechanism of the eagle owl （Bubo bubo） by Stereo Microscope （SM）, Scanning Electron Microscopy （SEM） and Laser Scanning Confocal Microscope （LSCM）. To investigate the effects of special charac- teristics of wing feather on owl silent flight, the acoustic properties, including the sound absorption coefficient and flight noise, were compared between the eagle owl and common buzzard （Buteo buteo）. The results show that the eagle owl generates lower noise than common buzzard during flight, and its wing feather has better sound absorption properties. The leading edge serration and trailing edge fringe can improve the pressure fluctuation of turbulence boundary, and suppress the generation of vortex sound. The elongated distal barbules form a multi-layer grid porous structure which also has an effect on sound absorption. This research not only can give the inspiration for solving the aerodynamic noise of aircraft and engineering machine, but also can provide a new idea for the design of low-noise devices.
文摘High-resolution Particle-Image Velocimetry （PIV） and time-resolved force measurements were performed to analyze the impact of the comb-like structure on the leading edge of barn owl wings on the flow field and overall aerodynamic performance. The Reynolds number was varied in the range of 40,000 to 120,000 and the range of angle of attack was 0° to 6° for the PIV and -15° to ＋20° for the force measurements to cover the full flight envelope of the owl. As a reference, a wind-tunnel model which possessed a geometry based on the shape of a typical barn owl wing without any owl-specific adaptations was built, and measurements were performed in the aforementioned Reynolds number and angle of attack： range. This clean wing model shows a separation bubble in the distal part of the wing at higher angles of attack. Two types of comb-like structures, i.e., artificial serrations, were manufactured to model the owl＇s leading edge with respect to its length, thickness, and material properties. The artificial structures were able to reduce the size of the separation region and additionally cause a more uniform size of the vortical structures shed by the separation bubble within the Reynolds number range investigated, resulting in stable gliding flight independent of the flight velocity. However, due to increased drag coefficients in conjunction with similar lift coefficients, the overall aerodynamic performance, i.e., lift-to-drag ratio is reduced for the serrated models. Nevertheless, especially at lower Reynolds numbers the stabilizing effect of the uniform vortex size outperforms the lower aerodynamic performance.
文摘采用大涡模拟技术对长耳鸮翅膀展向20%、40%和60%截面处翼型的非定常湍流场进行数值模拟,并基于Lighthill声类比方法对非定常流场诱导的声场进行计算,研究上述仿生翼型的气动与声学性能。研究结果表明:三种仿生翼型均具有高升阻比特性,其中20%、40%截面处翼型的升力系数较高,5°攻角下分别为1.86和1.72;20%截面处翼型阻力系数最高,且在强烈的逆压梯度下,20%和40%截面处翼型气流在压力面前缘开始分离,在下游处自由剪切层产生了明显的不规则涡结构;翼型尾缘处,涡流脱落后在尾迹区发生涡结构破碎;60%截面处翼型载荷分布最均匀,附面层增长缓慢,因而该翼型流场的涡量相对较小,使得其诱导噪声较低。声学计算结果表明,三种仿生翼型的最大声压级分别为85.8、78.6和74.8 d B。
基金Tile authors gratefully acknowledge the support of the National Natural Science Foundation of China （Grant No.31071928）, NSFC Projects of Joint fund of high-speed Train Basic Research （Grant No. U1134109）, NSFC Projects of International Cooperation and Exchanges （Grant No. 50920105504）, and the Youth Research Foundation of the Jilin University Agronomy Faculty （Grant No. 4305050102k7）.
文摘Flow control can effectively reduce the aerodynamic noise radiated from a circular cylinder. As one of the flow control methods, a bionic method, inspired by the serrations at the leading edge of owls＇ wing, was proposed in this paper. The effects of bionic serrated structures arranged on the upper and lower sides of a cylinder on the aerodynamic and aeroacoustic performance of the cylinder were numerically investigated. At a free stream speed of 24.5 m.s-1, corresponding to Reynolds number of 1.58 × 10^4, the simulation results indicate that the bionic serrated structures can decrease the frequency of the vortex shedding and control the fluctuating aerodynamic force acting on the cylinder, thus reduce the aerodynamic noise. A qualitative view of the vorticity in the wake of the cylinder suggest that the serrated structures reduce aerodynamic sound by suppressing the unsteady motion of vortices.
