Article
Engineering, Aerospace
Alex Zanotti, Davide Algarotti
Summary: This article investigates the aerodynamic interaction between front and rear propellers during the flight of eVTOLs and its impact on propeller performance and flow field. Wind tunnel tests and numerical simulations reveal that an increased degree of overlapping between the propeller disks leads to a significant loss of rear propeller thrust, and partial overlapping results in higher thrust fluctuations.
AEROSPACE SCIENCE AND TECHNOLOGY
(2022)
Review
Thermodynamics
H. Y. Peng, H. J. Liu, J. H. Yang
Summary: Vertical axis wind turbines (VAWTs) have unique attributes such as exceptional performance in built environments and high packing density in wind farms. This study reviews recent research on the wake aerodynamics of H-rotor VAWTs, presenting mathematical expressions and a classic aerodynamic model for rotor analysis. The wakes of VAWTs are characterized by distinctive features like strong asymmetry and counter-rotating vortical motion, which have led to the development of various wake models for standalone VAWTs or multiple VAWT layouts. Researchers have used a wide range of methods, including wind tunnel testing, PIV tests, field tests, CFD simulations, and theoretical development, to investigate the wake flow fields and vortical structures of VAWTs.
Article
Engineering, Aerospace
Alex Zanotti
Summary: This article presents the results of a wind tunnel study on the aerodynamic interaction between side-by-side propellers in cruise flight conditions of eVTOLs. Stereo particle image velocimetry (PIV) measurements were used to provide detailed insights into the flow physics of the interacting propellers, focusing on the effects on tip vortices and wake topology at different advance ratios.
Article
Engineering, Civil
Dipesh Patel, Andrew Garmory, Martin Passmore
Summary: The wake of an isolated, rotating wheel in open-wheel motorsport was investigated using CFD and compared with data from PIV wind tunnel experiments. The results show significant differences in the wake topology between the two methods. The wake consists of incoherent macro-scale eddies and deformed counter-rotating vortices. Analysis also reveals significant transverse and vertical velocity fluctuations in the wake.
JOURNAL OF WIND ENGINEERING AND INDUSTRIAL AERODYNAMICS
(2022)
Article
Biology
Kajsa Warfvinge, L. Christoffer Johansson, Anders Hedenstrom
Summary: This study used tomographic particle image velocimetry to show that the wake shed by hovering hawkmoths is best described as a series of bilateral, stacked vortex 'rings'. Despite aerodynamically active upstroke with an inclined stroke plane, it produces weaker vortices than the downstroke, and the far wake lacks structure and is less concentrated compared with the near wake. The wake topologies of both near and far wakes are clearly affected by vortex interactions, suggesting caution is required when interpreting wake structures.
JOURNAL OF EXPERIMENTAL BIOLOGY
(2021)
Article
Biology
Geoffrey Ruaux, Kyra Monmasson, Tyson L. Hedrick, Sophie Lumineau, Emmanuel de Margerie
Summary: Birds, such as the common swift, have evolved energy-saving strategies during flight, including the touch-and-go drinking behavior. However, our study found that the swifts do not increase their speed when approaching a water surface with higher mechanical energy, but instead brake to reduce height and speed. This behavior is possibly a trade-off between energy expenditure and safety, as high speed increases the risk of falling into water.
JOURNAL OF EXPERIMENTAL BIOLOGY
(2023)
Article
Thermodynamics
Guiyue Duan, Arslan Salim Dar, Fernando Porte-Agel
Summary: This study uses wind tunnel experiments to investigate cyclic yaw control as a wake mitigation strategy to improve power production in wind farms. The control strategy is applied to single and multiple wind turbines, and the power performance is optimized by adjusting control parameters. Results show that cyclic yaw control can achieve a power gain of over 10% compared to uncontrolled wind farms. The control power consumed is small and predictable, and wake measurements demonstrate improved wake velocity deficit profiles and faster wake recovery.
ENERGY CONVERSION AND MANAGEMENT
(2023)
Article
Engineering, Marine
Kwan Pui Mok, Peng Zhou, Jiafan Hou, Siyang Zhong, Xin Zhang, Raymond Chi-Hung So, King Yin Chan
Summary: This research investigates the aerodynamic forces and moments acting on a windsurfing sail during steady sailing, and has found that the rig-back angle has significant effects on the performance of the sail.
Article
Biotechnology & Applied Microbiology
Liansong Peng, Tianyu Pan, Mengzong Zheng, Shiying Song, Guanting Su, Qiushi Li
Summary: This study presents a detailed analysis of dragonflies' climbing flight by integrating high-speed photogrammetry, three-dimensional reconstruction, and computational fluid dynamics. The research reveals the relationship between climbing angle and wing kinematics, as well as the significant impact of different wing kinematics on aerodynamic performance.
FRONTIERS IN BIOENGINEERING AND BIOTECHNOLOGY
(2022)
Article
Physics, Fluids & Plasmas
Yu Zhu Lyu, Mao Sun
Summary: This study investigates the effects of insect size on the longitudinal flight dynamic stability of insects. The results show that although there is a considerable difference in mass, the flight stability mode remains the same for insects of different sizes. However, as the size decreases, the instability becomes faster, requiring a faster nervous system to control the flight.
Article
Multidisciplinary Sciences
Kambiz Salari, Jason M. Ortega
Summary: By using wind tunnel measurements and computational fluid dynamics simulations, a vehicle design has been demonstrated to generate negative body-axis drag in crosswinds, resulting in lower drag coefficients and potentially reducing petroleum usage in the heavy vehicle industry.
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
(2021)
Article
Marine & Freshwater Biology
Ian K. Bartol, Alissa M. Ganley, Amanda N. Tumminelli, Soraya M. Bartol, Joseph T. Thompson, Paul S. Krueger
Summary: Turning plays a crucial role in ecological success in the oceans, allowing squids to capture prey, escape predators, and navigate complex environments. However, there is limited quantitative knowledge about their turning dynamics. This study examined the turning capacity of neritic squids, focusing on the role of propulsors and orientation, and investigated if jet flow can predict their performance. The results showed that Lolliguncula brevis was the most proficient at turning, with the highest angular velocity and the lowest turning radius. The pulsed jet was found to contribute significantly to turns in all squids, and the direction of the turns and jet velocity/impulse were key factors affecting turning performance.
Article
Mechanics
Fei Wang, Chun-Ho Liu, Jingwei Xie
Summary: This study conducted a large-eddy simulation to investigate turbulent pollutant dispersion in the near wake behind a real, light-duty lorry, with results comparing favorably with simplified vehicle models in the literature. By using proper orthogonal decomposition (POD), flow instabilities in the vertical and horizontal directions, as well as pumping motion, were identified with characteristic frequencies. Additionally, coherence analysis revealed strong modulation behavior and the evolution of the lower vortex system spirally and in-phase near the ground.
Article
Biology
Shannon E. Currie, L. Christoffer Johansson, Cedric Aumont, Christian C. Voigt, Anders Hedenstrom
Summary: The efficiency of converting metabolic power to mechanical power in flying animals is important for their flight behavior and energy requirements. However, there is a lack of empirical data on conversion efficiency for most species, making it difficult to measure in vivo. This study shows that conversion efficiency in the migratory bat increases with flight speed, suggesting that it peaks near maximum range speed. The findings also reveal a positive scaling relationship between estimated conversion efficiency and body mass in birds and bats.
PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES
(2023)
Article
Energy & Fuels
Ondrej Fercak, Juliaan Bossuyt, Naseem Ali, Raul Bayoan Cal
Summary: The interest and benefits of offshore wind energy have led to challenges in understanding the dynamics of wind-turbine wakes and their interaction with the atmospheric boundary layer and surface waves. This study uses experimental methods to establish a better understanding of these interactions, providing insights into offshore wind-energy dynamics.
Biographical-Item
Biology
Anders Hedenstrom, Geoffrey Spedding
JOURNAL OF EXPERIMENTAL BIOLOGY
(2020)
Article
Biology
Linus Hedh, Christopher G. Guglielmo, L. Christoffer Johansson, Jessica E. Deakin, Christian C. Voigt, Anders Hedenstroem
JOURNAL OF EXPERIMENTAL BIOLOGY
(2020)
Article
Biology
Kajsa Warfvinge, L. Christoffer Johansson, Anders Hedenstrom
Summary: This study used tomographic particle image velocimetry to show that the wake shed by hovering hawkmoths is best described as a series of bilateral, stacked vortex 'rings'. Despite aerodynamically active upstroke with an inclined stroke plane, it produces weaker vortices than the downstroke, and the far wake lacks structure and is less concentrated compared with the near wake. The wake topologies of both near and far wakes are clearly affected by vortex interactions, suggesting caution is required when interpreting wake structures.
JOURNAL OF EXPERIMENTAL BIOLOGY
(2021)
Article
Multidisciplinary Sciences
Baptiste Garde, Rory P. Wilson, Emmanouil Lempidakis, Luca Borger, Steven J. Portugal, Anders Hedenstrom, Giacomo Dell'Omo, Michael Quetting, Martin Wikelski, Emily L. C. Shepard
Summary: The study found that homing pigeons exhibit some energy-saving strategies in adjusting flight speed and power allocation, but choose higher speeds during descending flight. These subtle variations in speed and altitude may be a form of protean behavior adopted to reduce predation risk.
ROYAL SOCIETY OPEN SCIENCE
(2021)
Article
Behavioral Sciences
Paula Hidalgo-Rodriguez, Pedro Saez-Gomez, Julio Blas, Anders Hedenstrom, Carlos Camacho
Summary: Body mass is an important indicator for migratory animals, with evidence showing that it influences migration decisions. A study on Red-necked Nightjars revealed that during the post-fledging period, both individual mass gain and selective disappearance of lighter individuals contribute to the increase in average body mass. The findings suggest caution in using population-level changes in body mass to infer individual fuel deposition rates.
BEHAVIORAL ECOLOGY
(2021)
Article
Ornithology
Anders Hedenstrom, Susanne Akesson, Staffan Bensch, Dennis Hasselquist, Ake Lindstrom
Summary: Seasonal timing of moult in migratory birds is an adaptation to cope with time constraints in the annual cycle, possibly largely under endogenous control. The researchers argue that previous analyses were flawed and overlooked key facts, such as the performance of juveniles in moult and the differences in moult sequences among different species.
Article
Mechanics
J. D. Tank, B. F. Klose, G. B. Jacobs, G. R. Spedding
Summary: By combining experimental and numerical studies, the importance of viscous dynamics in understanding the flow field and aerodynamic forces on a cambered airfoil is highlighted. The impact of angle of attack on flow states, including separation, instabilities, and transition to turbulence, is crucial for predicting lift and drag coefficients. Understanding the viscous dynamics of the boundary layer is essential for comprehending the aerodynamics at this scale, as elegantly described by Frank White.
Article
Behavioral Sciences
Linus Hedh, Juliana Danhardt, Anders Hedenstrom
Summary: Migration patterns and strategies of birds are influenced by environmental conditions and migration distances. Studying two populations of common ringed plover, researchers found differences in timing and speed of migration, suggesting that a combination of factors including population-specific migration timing, breeding season length, and proximity to breeding areas shape the annual cycle and migratory behaviors.
BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY
(2022)
Article
Biology
Gabriel Norevik, Susanne Akesson, Arne Andersson, Johan Backman, Anders Hedenstrom
Summary: Research found that European nightjars exhibit more exploratory vertical flights during spring migrations, including major climbs, greater vertical displacement, and less time spent in level flight. They typically operate at ascent rates below the theoretical maximum and descend actively rather than by gliding flight.
JOURNAL OF EXPERIMENTAL BIOLOGY
(2021)
Article
Mechanics
T. J. Madison, X. Xiang, G. R. Spedding
Summary: The study investigates the flow around and behind a sphere in a linear density gradient, serving as a model problem for body-generated wakes in atmospheres and oceans. Experimental and numerical simulations reveal the early wake affected by the background density gradient, leading to five distinguishable flow regimes that maintain their distinguishing features up to buoyancy times of 20.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Physics, Fluids & Plasmas
Chan-Ye Ohh, Geoffrey R. Spedding
Summary: This study investigates the wake characteristics behind a bluff body with a density gradient using dynamic mode decomposition (DMD) to find patterns for automated classification. The results show that the success of this method depends on the quality and dimension of input data, but the initial steps have achieved some level of success and can provide guidance for studying more complex turbulent wakes using data-driven methods.
PHYSICAL REVIEW FLUIDS
(2022)
Article
Physics, Fluids & Plasmas
Vamsi Krishna Chinta, Chan-Ye Ohh, Geoffrey Spedding, Mitul Luhar
Summary: This article presents a method for determining the dynamic state using limited measurement data, which reconstructs the velocity field using dynamic mode decomposition and orthogonal least squares algorithm, and estimates the dynamic state of the measurement data.
PHYSICAL REVIEW FLUIDS
(2022)
Review
Biology
Anders Hedenstrom
Summary: Vertebrates capable of flight, such as birds and bats, rely on wings, muscles, and sensory inputs to control their movement. Wing damage and loss of wing surface due to moult can significantly affect flight performance. Birds counteract the effects of moult through concurrent mass loss and enlarged flight muscles. Bats rely on sensory hairs and thread-like muscles in their wings, and wing damage can impair their flight speed and control of wing camber.
JOURNAL OF EXPERIMENTAL BIOLOGY
(2023)
Article
Biology
Shannon E. Currie, L. Christoffer Johansson, Cedric Aumont, Christian C. Voigt, Anders Hedenstrom
Summary: The efficiency of converting metabolic power to mechanical power in flying animals is important for their flight behavior and energy requirements. However, there is a lack of empirical data on conversion efficiency for most species, making it difficult to measure in vivo. This study shows that conversion efficiency in the migratory bat increases with flight speed, suggesting that it peaks near maximum range speed. The findings also reveal a positive scaling relationship between estimated conversion efficiency and body mass in birds and bats.
PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES
(2023)
Article
Multidisciplinary Sciences
Gabriel Norevik, Susanne Akesson, Anders Hedenstrom
Summary: Understanding the trade-off between carrying large fuel loads and the risk of fuel depletion is crucial in studying the migratory flight strategies of land-birds. European nightjars, when crossing water barriers during migration, have shown specific flight behaviors that enable them to save energy and reduce flight costs. By flying at a low altitude above the sea surface and using an energy-efficient flap-glide flight style, they can exploit local updrafts and pressure variations to their advantage.