scholarly journals Flow visualization and unsteady aerodynamics in the flight of the hawkmoth, Manduca sexta

1997 ◽  
Vol 352 (1351) ◽  
pp. 303-316 ◽  
Author(s):  
Alexander P. Willmott ◽  
Charles P. Ellington ◽  
Adrian L. R. Thomas
Keyword(s):  
Manduca Sexta ◽  
High Speed ◽  
Unsteady Aerodynamics ◽  
Leading Edge ◽  
Vortex Rings ◽  
Leading Edge Vortex ◽  
Smoke Visualization ◽  
Left Behind ◽  
Trailing Edges ◽  
Edge Vortex

The aerodynamic mechanisms employed durng the flight of the hawkmoth, Manduca sexta , have been investigated through smoke visualization studies with tethered moths. Details of the flow around the wings and of the overall wake structure were recorded as stereophotographs and high–speed video sequences. The changes in flow which accompanied increases in flight speed from 0.4 to 5.7 m s −1 were analysed. The wake consists of an alternating series of horizontal and vertical vortex rings which are generated by successive down– and upstrokes, respectively. The downstroke produces significantly more lift than the upstroke due to a leading–edge vortex which is stabilized by a radia flow moving out towards the wingtip. The leading–edge vortex grew in size with increasing forward flight velocity. Such a phenomenon is proposed as a likely mechanism for lift enhancement in many insect groups. During supination, vorticity is shed from the leading edge as postulated in the ‘flex’ mechanism. This vorticity would enhance upstroke lift if it was recaptured diring subsequent translation, but it is not. Instead, the vorticity is left behind and the upstroke circulation builds up slowly. A small jet provides additional thrust as the trailing edges approach at the end of the upstroke. The stereophotographs also suggest that the bound circulation may not be reversed between half strokes at the fastest flight speeds.

scholarly journals A computational fluid dynamic study of hawkmoth hovering

1998 ◽  
Vol 201 (4) ◽  
pp. 461-477 ◽  
Author(s):  
H Liu ◽  
C P Ellington ◽  
K Kawachi ◽  
C van den Berg ◽  
A P Willmott
Keyword(s):  
Fluid Dynamic ◽  
Translational Motion ◽  
Three Dimensional ◽  
Axial Flow ◽  
Unsteady Aerodynamics ◽  
Leading Edge ◽  
Flapping Wing ◽  
Leading Edge Vortex ◽  
Edge Vortex ◽  
Rotational Motions

A computational fluid dynamic (CFD) modelling approach is used to study the unsteady aerodynamics of the flapping wing of a hovering hawkmoth. We use the geometry of a Manduca sexta-based robotic wing to define the shape of a three-dimensional 'virtual' wing model and 'hover' this wing, mimicking accurately the three-dimensional movements of the wing of a hovering hawkmoth. Our CFD analysis has established an overall understanding of the viscous and unsteady flow around the flapping wing and of the time course of instantaneous force production, which reveals that hovering flight is dominated by the unsteady aerodynamics of both the instantaneous dynamics and also the past history of the wing. <P> A coherent leading-edge vortex with axial flow was detected during translational motions of both the up- and downstrokes. The attached leading-edge vortex causes a negative pressure region and, hence, is responsible for enhancing lift production. The axial flow, which is derived from the spanwise pressure gradient, stabilises the vortex and gives it a characteristic spiral conical shape. <P> The leading-edge vortex created during previous translational motion remains attached during the rotational motions of pronation and supination. This vortex, however, is substantially deformed due to coupling between the translational and rotational motions, develops into a complex structure, and is eventually shed before the subsequent translational motion. <P> Estimation of the forces during one complete flapping cycle shows that lift is produced mainly during the downstroke and the latter half of the upstroke, with little force generated during pronation and supination. The stroke plane angle that satisfies the horizontal force balance of hovering is 23.6 degrees , which shows excellent agreement with observed angles of approximately 20-25 degrees . The time-averaged vertical force is 40 % greater than that needed to support the weight of the hawkmoth.

scholarly journals The vortex wake of a ‘hovering’ model hawkmoth

1997 ◽  
Vol 352 (1351) ◽  
pp. 317-328 ◽  
Author(s):  
Coen van den Berg ◽  
Charles P. Ellington
Keyword(s):  
Lift Force ◽  
Three Dimensional ◽  
Axial Flow ◽  
Leading Edge ◽  
The Body ◽  
Tip Vortex ◽  
Vortex Rings ◽  
Leading Edge Vortex ◽  
Edge Vortex ◽  
Visualization Experiments

Visualization experiments with Manduca sexta have revealed the presence of a leading–edge vortex and a highly three–dimensional flow pattern. To further investigate this important discovery, a scaled–up robotic insect was built (the ‘flapper’) which could mimic the complex movements of the wings of a hovering hawkmoth. Smoke released from the leading edge of the flapper wing revealed a small but strong leading–edge vortex on the downstroke. This vortex had a high axial flow velocity and was stable, separating from the wing at approximately 75 % of the wing length. It connected to a large, tangled tip vortex, extending back to a combining stopping and starting vortex from pronation. At the end of the downstroke, the wake could be approximated as one vortex ring per wing. Based on the size and velocity of the vortex rings, the mean lift force during the downstroke was estimated to be about 1.5 times the body weight of a hawkmoth, confirming that the downstroke is the main provider of lift force.

scholarly journals Hawkmoth flight in the unsteady wakes of flowers

2018 ◽  
Author(s):  
Megan Matthews ◽  
Simon Sponberg
Keyword(s):  
Leading Edge ◽  
Low Frequencies ◽  
Reduced Order ◽  
Leading Edge Vortex ◽  
Smoke Visualization ◽  
Flight Chamber ◽  
Wind Gusts ◽  
3D Printed ◽  
Edge Vortex ◽  
Summary Statement

AbstractFlying animals maneuver and hover through environments where wind gusts and flower wakes produce unsteady flow. Although both flight maneuvers and aerodynamic mechanisms have been studied independently, little is known about how these interact in an environment where flow is already unsteady. Moths forage from flowers by hovering in the flower’s wake. We investigate hawkmoths tracking a 3D-printed robotic flower in a wind tunnel. We visualize the flow in the wake and around the wings and compare tracking performance to previous experiments in a still air flight chamber. Like in still air, moths flying in the flower wake exhibit near perfect tracking at low frequencies where natural flowers move. However, tracking in the flower wake results in a larger overshoot between 2-5 Hz. System identification of flower tracking reveals that moths also display reduced-order dynamics in wind, compared to still air. Smoke visualization of the flower wake shows that the dominant vortex shedding corresponds to the same frequency band as the increased overshoot. Despite these large effects on tracking dynamics in wind, the leading edge vortex (LEV) remains bound to the wing throughout the wingstroke and does not burst. The LEV also maintains the same qualitative structure seen in steady air. Persistence of a stable LEV during decreased flower tracking demonstrates the interplay between hovering and maneuvering.Summary statementWe examined how moths maneuver in the wake of flowers and discover that flower tracking dynamics are simplified compared to still air, while the leading edge vortex does not burst and extends continuously across the wings and thorax.

Flight

2018 ◽  
Author(s):  
Anders Hedenström
Keyword(s):  
Bird Species ◽  
Leading Edge ◽  
Micro Air Vehicles ◽  
Leading Edge Vortex ◽  
Confined Spaces ◽  
Unsteady Aerodynamic ◽  
Maneuvering Flight ◽  
Edge Vortex ◽  
Lifting Surfaces ◽  
Animal Flight

Animal flight represents a great challenge and model for biomimetic design efforts. Powered flight at low speeds requires not only appropriate lifting surfaces (wings) and actuator (engine), but also an advanced sensory control system to allow maneuvering in confined spaces, and take-off and landing. Millions of years of evolutionary tinkering has resulted in modern birds and bats, which are achieve controlled maneuvering flight as well as hovering and cruising flight with trans-continental non-stop migratory flights enduring several days in some bird species. Unsteady aerodynamic mechanisms allows for hovering and slow flight in insects, birds and bats, such as for example the delayed stall with a leading edge vortex used to enhance lift at slows speeds. By studying animal flight with the aim of mimicking key adaptations allowing flight as found in animals, engineers will be able to design micro air vehicles of similar capacities.

Flow criticality governs leading-edge-vortex initiation on finite wings in unsteady flow

2021 ◽  
Vol 910 ◽  
Author(s):  
Yoshikazu Hirato ◽  
Minao Shen ◽  
Ashok Gopalarathnam ◽  
Jack R. Edwards
Keyword(s):  
Unsteady Flow ◽  
Leading Edge ◽  
Leading Edge Vortex ◽  
Edge Vortex

Abstract

Vorticity transport in the leading-edge vortex on a rotating blade

2014 ◽  
Vol 743 ◽  
pp. 249-261 ◽  
Author(s):  
Craig J. Wojcik ◽  
James H. J. Buchholz
Keyword(s):  
Leading Edge ◽  
Quasi Equilibrium ◽  
Transport Mechanisms ◽  
Leading Edge Vortex ◽  
Rotating Blade ◽  
Edge Vortex ◽  
Rotation Motion ◽  
Vorticity Transport ◽  
Control Volumes ◽  
Quiescent Fluid

AbstractVorticity transport is analysed within the leading-edge vortex generated on a rectangular flat plate of aspect ratio 4 undergoing a starting rotation motion in a quiescent fluid. Two analyses are conducted on the inboard half of the blade to better understand the vorticity transport mechanisms responsible for maintaining the quasi-equilibrium state of the leading-edge vortex. An initial global analysis between the $25$ and $50\, \%$ spanwise positions suggests that, although spanwise velocity is significant, spanwise convection of vorticity is insufficient to balance the flux of vorticity from the leading-edge shear layer. Subsequent detailed analyses of vorticity transport in planar control volumes at the $25$ and $50\, \%$ spanwise positions verify this conclusion and demonstrate that vorticity annihilation due to interaction between the leading-edge vortex and the opposite-sign layer on the plate surface is an important, often dominant, mechanism for regulation of leading-edge-vortex circulation. Thus, it provides an important condition for maintenance of an attached leading-edge vortex on the inboard portion of the blade.

Heat Transfer and Flowfield Measurements in the Leading Edge Region of a Stator Vane Endwall

1999 ◽  
Vol 121 (3) ◽  
pp. 558-568 ◽  
Author(s):  
M. B. Kang ◽  
A. Kohli ◽  
K. A. Thole
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Edge Region ◽  
Leading Edge Vortex ◽  
Stator Vane ◽  
Edge Vortex ◽  
The Mean

The leading edge region of a first-stage stator vane experiences high heat transfer rates, especially near the endwall, making it very important to get a better understanding of the formation of the leading edge vortex. In order to improve numerical predictions of the complex endwall flow, benchmark quality experimental data are required. To this purpose, this study documents the endwall heat transfer and static pressure coefficient distribution of a modern stator vane for two different exit Reynolds numbers (Reex = 6 × 105 and 1.2 × 106). In addition, laser-Doppler velocimeter measurements of all three components of the mean and fluctuating velocities are presented for a plane in the leading edge region. Results indicate that the endwall heat transfer, pressure distribution, and flowfield characteristics change with Reynolds number. The endwall pressure distributions show that lower pressure coefficients occur at higher Reynolds numbers due to secondary flows. The stronger secondary flows cause enhanced heat transfer near the trailing edge of the vane at the higher Reynolds number. On the other hand, the mean velocity, turbulent kinetic energy, and vorticity results indicate that leading edge vortex is stronger and more turbulent at the lower Reynolds number. The Reynolds number also has an effect on the location of the separation point, which moves closer to the stator vane at lower Reynolds numbers.

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