scholarly journals Comparative aerodynamic performance of flapping flight in two bat species using time-resolved wake visualization

2011 ◽  
Vol 8 (63) ◽  
pp. 1418-1428 ◽  
Author(s):  
Florian T. Muijres ◽  
L. Christoffer Johansson ◽  
York Winter ◽  
Anders Hedenström
Keyword(s):  
Movement Ecology ◽  
Ecological Factors ◽  
Reynolds Numbers ◽  
Aerodynamic Performance ◽  
Flight Performance ◽  
Flexible Wings ◽  
Time Resolved ◽  
Image Velocimetry ◽  
Bat Wing ◽  
Wing Performance

Bats are unique among extant actively flying animals in having very flexible wings, controlled by multi-jointed fingers. This gives the potential for fine-tuned active control to optimize aerodynamic performance throughout the wingbeat and thus a more efficient flight. But how bat wing performance scales with size, morphology and ecology is not yet known. Here, we present time-resolved fluid wake data of two species of bats flying freely across a range of flight speeds using stereoscopic digital particle image velocimetry in a wind tunnel. From these data, we construct an average wake for each bat species and speed combination, which is used to estimate the flight forces throughout the wingbeat and resulting flight performance properties such as lift-to-drag ratio ( L/D ). The results show that the wake dynamics and flight performance of both bat species are similar, as was expected since both species operate at similar Reynolds numbers ( Re ) and Strouhal numbers ( St ). However, maximum L/D is achieved at a significant higher flight speed for the larger, highly mobile and migratory bat species than for the smaller non-migratory species. Although the flight performance of these bats may depend on a range of morphological and ecological factors, the differences in optimal flight speeds between the species could at least partly be explained by differences in their movement ecology.

Entrainment and topology of accelerating shear layers

2016 ◽  
Vol 811 ◽  
pp. 37-50 ◽  
Author(s):  
Giuseppe A. Rosi ◽  
David E. Rival
Keyword(s):  
Shear Layer ◽  
Particle Image ◽  
Point Vortex ◽  
Reynolds Numbers ◽  
Shear Layers ◽  
Circular Path ◽  
Entrainment Rate ◽  
Time Resolved ◽  
And Topology ◽  
Image Velocimetry

A constantly accelerating circular plate was investigated towards understanding the effect of non-stationarity on shear-layer entrainment and topology. Dye visualizations and time-resolved particle image velocimetry measurements were collected for normalized accelerations spanning three orders of magnitude. Increasing acceleration acts to organize shear-layer topology. Specifically, the Kelvin–Helmholtz instabilities within the shear layer better adhered to a circular path and exhibited consistent and repeatable spacing. Normalized starting-vortex circulation was observed to collapse with increasing acceleration, which one might not expect due to increased levels of mixing at higher instantaneous Reynolds numbers. The entrainment rate was shown to increase nonlinearly with increasing acceleration. This was attributed to closer spacing between instabilities, which better facilitates the roll-up of fluid between the shear layer and vortex core. The shear-layer organization observed at higher accelerations was associated with smaller spacings between instabilities. Specifically, analogous point-vortex simulations demonstrated that decreasing the spacing between instabilities acts to localize and dampen perturbations within an accelerating shear layer.

scholarly journals Evolution of Turbulent Horseshoe Vortex System in Front of a Vertical Circular Cylinder in Open Channel

Water ◽  
2019 ◽  
Vol 11 (10) ◽  
pp. 2079 ◽  
Author(s):  
Chen ◽  
Yang ◽  
Wu
Keyword(s):  
Open Channel ◽  
Evolutionary Process ◽  
Reynolds Numbers ◽  
Horseshoe Vortex ◽  
Local Scour ◽  
Time Resolved ◽  
Vortex Interactions ◽  
Initial Stage ◽  
Image Velocimetry ◽  
Underlying Mechanisms

A turbulent horseshoe vortex (HV) system around a wall-mounted cylinder in open channel is characterized by random variations in vortex features and an abundance of vortex interactions. The turbulent HV system is responsible for initiating the local scour process in front of the cylinder. The evolution of the turbulent HV system is investigated statistically and quantitatively with time-resolved particle image velocimetry. The cylinder Reynolds numbers of the flow are 8600, 10,200, and 13,600, respectively. A novel vortex tracking method was proposed to obtain the variations in position, size, and strength of the primary HV (PHV) which dominates the system most of the time. Relationships between the various features of the PHV during its evolutionary process were obtained through correlation analyses. Results show that the dimensionless mean lifespan of the PHV is about 5.0. Statistically, the downstream movement of the PHV toward the cylinder is accompanied with its bed-approaching movement and decreasing in size, and the opposite is true. The circulation strength of the PHV decreases and increases dramatically in the region downstream of its time-averaged position when the PHV approaches and departs from the cylinder, respectively. Meanwhile, mechanisms responsible for the generation, movement, variation, and disappearance of the PHV are re-investigated and enriched based on its interactions with vortices in the separation region and structures in the incoming flow. The obtained change trends of the features of the PHV and the underlying mechanisms for its evolution are valuable for predicting and controlling the initial stage of the local scour in front of cylinders.

scholarly journals Simulation Analysis of the Aerodynamic Performance of a Bionic Aircraft with Foldable Beetle Wings in Gliding Flight

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Caidong Wang ◽  
Yu Ning ◽  
Xinjie Wang ◽  
Junqiu Zhang ◽  
Liangwen Wang
Keyword(s):  
Simulation Analysis ◽  
Simulation Method ◽  
Aerodynamic Characteristics ◽  
Aerodynamic Performance ◽  
Elastic Model ◽  
Flight Performance ◽  
Flexible Wings ◽  
Gliding Flight ◽  
Drag Ratio ◽  
Gliding Movement

Beetles have excellent flight performance. Based on the four-plate mechanism theory, a novel bionic flapping aircraft with foldable beetle wings was designed. It can perform flapping, gliding, wing folding, and abduction/adduction movements with a self-locking function. In order to study the flight characteristics of beetles and improve their gliding performance, this paper used a two-way Fluid-Structure Interaction (FSI) numerical simulation method to focus on the gliding performance of the bionic flapping aircraft. The effects of elastic model, rigid and flexible wing, angle of attack, and velocity on the aerodynamic characteristics of the aircraft in gliding flight are analyzed. It was found that the elastic modulus of the flexible hinges has little effect on the aerodynamic performance of the aircraft. Both the rigid and the flexible wings have a maximum lift-to-drag ratio when the attack angle is 10°. The lift increased with the increase of the gliding speed, and it was found that the lift cannot support the gliding movement at low speeds. In order to achieve gliding, considering the weight and flight performance, the weight of the microair vehicle is controlled at about 3 g, and the gliding speed is guaranteed to be greater than 6.5 m/s. The results of this study are of great significance for the design of bionic flapping aircrafts.

Experimental Study of Jet Flow Impingement Within a Rod Bundle Using PIV Technique

2008 ◽  
Author(s):  
Noushin Amini ◽  
Yassin A. Hassan
Keyword(s):  
Particle Image ◽  
Rectangular Channel ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Reynolds Stresses ◽  
Particle Image Velocimetry Technique ◽  
Time Resolved ◽  
Rod Bundle ◽  
Piv Technique ◽  
Image Velocimetry

In this investigation Particle Image Velocimetry technique was implemented to a matched refractive index facility which was placed in a rectangular channel of L:1016 mm×W:76.2 mm×H:76.2 mm. Water was pumped into either one or both of the inlet jets which were entering the channel’s top wall with several different Reynolds numbers. The instantaneous and time-resolved velocity fields were successfully obtained from which several flow characteristics such as vorticity, turbulence instabilities and Reynolds stresses can be calculated.

scholarly journals A novel cylindrical overlap-and-fling mechanism used by sea butterflies

2020 ◽  
Vol 223 (15) ◽  
pp. jeb221499 ◽  
Author(s):  
Ferhat Karakas ◽  
Amy E. Maas ◽  
David W. Murphy
Keyword(s):  
High Speed ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Flexible Wings ◽  
Micro Particle Image Velocimetry ◽  
Flying Insects ◽  
Marine Snails ◽  
Image Velocimetry ◽  
Edge Vortex ◽  
Generation Mechanisms

ABSTRACTThe clap-and-fling mechanism is a well-studied, unsteady lift generation mechanism widely used by flying insects and is considered obligatory for tiny insects flying at low to intermediate Reynolds numbers, Re. However, some aquatic zooplankters including some pteropod (i.e. sea butterfly) and heteropod species swimming at low to intermediate Re also use the clap-and-fling mechanism. These marine snails have extremely flexible, actively deformed, muscular wings which they flap reciprocally to create propulsive force, and these wings may enable novel lift generation mechanisms not available to insects, which have less flexible, passively deformed wings. Using high-speed stereophotogrammetry and micro-particle image velocimetry, we describe a novel cylindrical overlap-and-fling mechanism used by the pteropod species Cuvierina atlantica. In this maneuver, the pteropod's wingtips overlap at the end of each half-stroke to sequentially form a downward-opening cone, a cylinder and an upward-opening cone. The transition from downward-opening cone to cylinder produces a downward-directed jet at the trailing edges. Similarly, the transition from cylinder to upward-opening cone produces downward flow into the gap between the wings, a leading edge vortex ring and a corresponding sharp increase in swimming speed. The ability of this pteropod species to perform the cylindrical overlap-and-fling maneuver twice during each stroke is enabled by its slender body and highly flexible wings. The cylindrical overlap-and-fling mechanism observed here may inspire the design of new soft robotic aquatic vehicles incorporating highly flexible propulsors to take advantage of this novel lift generation technique.

Airfoil Section Characteristics at a Low Reynolds Number

1997 ◽  
Vol 119 (1) ◽  
pp. 129-135 ◽  
Author(s):  
Shigeru Sunada ◽  
Akitoshi Sakaguchi ◽  
Keiji Kawachi
Keyword(s):  
Reynolds Number ◽  
Three Dimensional ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Aerodynamic Characteristics ◽  
Aerodynamic Performance ◽  
Flight Performance ◽  
High Reynolds ◽  
Shape Characteristics ◽  
Sharp Leading Edge

The aerodynamic characteristics of airfoils operating at Re = 4 × 103 were examined, varying the parameters related to the airfoil shape such as thickness, camber, and roughness. Airfoils with good aerodynamic performance at this Re have the following shape characteristics: (1) they are thinner than airfoils for higher Re numbers, (2) they have a sharp leading edge, and (3) they have a camber of about five percent with its maximum camber at about mid-chord. The characteristics of airfoils are strongly affected by leading edge vortices. The measured two-dimensional airfoil characteristics indicate that the planform, which greatly affects the flight performance of the three-dimensional wing at high Reynolds numbers, has little effect on the flight performance at this Reynolds number.

Investigation on the effect of leading edge tubercles of sweptback wing at low reynolds number

2020 ◽  
Vol 21 (6) ◽  
pp. 621
Author(s):  
Veerapathiran Thangaraj Gopinathan ◽  
John Bruce Ralphin Rose ◽  
Mohanram Surya
Keyword(s):  
Leading Edge ◽  
Reynolds Numbers ◽  
Sweep Angle ◽  
Laminar Separation ◽  
Low Reynolds Numbers ◽  
Flow Energy ◽  
Airplane Wing ◽  
Low Reynolds ◽  
Naca 0015 ◽  
Wing Performance

Aerodynamic efficiency of an airplane wing can be improved either by increasing its lift generation tendency or by reducing the drag. Recently, Bio-inspired designs have been received greater attention for the geometric modifications of airplane wings. One of the bio-inspired designs contains sinusoidal Humpback Whale (HW) tubercles, i.e., protuberances exist at the wing leading edge (LE). The tubercles have excellent flow control characteristics at low Reynolds numbers. The present work describes about the effect of tubercles on swept back wing performance at various Angle of Attack (AoA). NACA 0015 and NACA 4415 airfoils are used for swept back wing design with sweep angle about 30°. The modified wings (HUMP 0015 A, HUMP 0015 B, HUMP 4415 A, HUMP 4415 B) are designed with two amplitude to wavelength ratios (η) of 0.1 & 0.24 for the performance analysis. It is a novel effort to analyze the tubercle vortices along the span that induce additional flow energy especially, behind the tubercles peak and trough region. Subsequently, Co-efficient of Lift (CL), Co-efficient of Drag (CD) and boundary layer pressure gradients also predicted for modified and baseline (smooth LE) models in the pre & post-stall regimes. It was observed that the tubercles increase the performance of swept back wings by the enhanced CL/CD ratio in the pre-stall AoA region. Interestingly, the flow separation region behind the centerline of tubercles and formation of Laminar Separation Bubbles (LSB) were asymmetric because of the sweep.

scholarly journals Time-resolved particle image velocimetry measurements of the turbulent Richtmyer–Meshkov instability

2021 ◽  
Vol 917 ◽  
Author(s):  
Everest G. Sewell ◽  
Kevin J. Ferguson ◽  
Vitaliy V. Krivets ◽  
Jeffrey W. Jacobs
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Time Resolved ◽  
Image Velocimetry

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