scholarly journals Squids use multiple escape jet patterns throughout ontogeny

Biology Open ◽  
2020 ◽  
Vol 9 (11) ◽  
pp. bio054585
Author(s):  
Carly A. York ◽  
Ian K. Bartol ◽  
Paul S. Krueger ◽  
Joseph T. Thompson
Keyword(s):  
Vortex Ring ◽  
High Speed ◽  
Leading Edge ◽  
High Volume ◽  
Mantle Cavity ◽  
Life Stages ◽  
Propulsive Efficiency ◽  
Vortex Ring Formation ◽  
Edge Vortex ◽  
Rapid Expulsion

ABSTRACTThroughout their lives, squids are both predators and prey for a multitude of animals, many of which are at the top of ocean food webs, making them an integral component of the trophic structure of marine ecosystems. The escape jet, which is produced by the rapid expulsion of water from the mantle cavity through a funnel, is central to a cephalopod's ability to avoid predation throughout its life. Although squid undergo morphological and behavioral changes and experience remarkably different Reynolds number regimes throughout their development, little is known about the dynamics and propulsive efficiency of escape jets throughout ontogeny. We examine the hydrodynamics and kinematics of escape jets in squid throughout ontogeny using 2D/3D velocimetry and high-speed videography. All life stages of squid produced two escape jet patterns: (1) ‘escape jet I’ characterized by short rapid pulses resulting in vortex ring formation and (2) ‘escape jet II’ characterized by long high-volume jets, often with a leading-edge vortex ring. Paralarvae exhibited higher propulsive efficiency than adult squid during escape jet ejection, and propulsive efficiency was higher for escape jet I than escape jet II in juveniles and adults. These results indicate that although squid undergo major ecological transitions and morphology changes from paralarvae to adults, all life stages demonstrate flexibility in escape jet responses and produce escape jets of surprisingly high propulsive efficiency.This article has an associated First Person interview with the first author of the paper.

scholarly journals Computational investigation of cicada aerodynamics in forward flight

2015 ◽  
Vol 12 (102) ◽  
pp. 20141116 ◽  
Author(s):  
Hui Wan ◽  
Haibo Dong ◽  
Kuo Gai
Keyword(s):  
Vortex Ring ◽  
High Speed ◽  
Three Dimensional ◽  
Leading Edge ◽  
Ring Structure ◽  
Forward Flight ◽  
Edge Vortex ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations ◽  
Wing Tip

Free forward flight of cicadas is investigated through high-speed photogrammetry, three-dimensional surface reconstruction and computational fluid dynamics simulations. We report two new vortices generated by the cicada's wide body. One is the thorax-generated vortex, which helps the downwash flow, indicating a new phenomenon of lift enhancement. Another is the cicada posterior body vortex, which entangles with the vortex ring composed of wing tip, trailing edge and wing root vortices. Some other vortex features include: independently developed left- and right-hand side leading edge vortex (LEV), dual-core LEV structure at the mid-wing region and near-wake two-vortex-ring structure. In the cicada forward flight, approximately 79% of the total lift is generated during the downstroke. Cicada wings experience drag in the downstroke, and generate thrust during the upstroke. Energetics study shows that the cicada in free forward flight consumes much more power in the downstroke than in the upstroke, to provide enough lift to support the weight and to overcome drag to move forward.

Effect of pectoral fin kinematics on manta ray propulsion

2018 ◽  
Vol 32 (12n13) ◽  
pp. 1840025
Author(s):  
Hao Lu ◽  
Khoon Seng Yeo ◽  
Chee-Meng Chew
Keyword(s):  
Leading Edge ◽  
Wave Model ◽  
Pectoral Fin ◽  
Long Distance ◽  
Propulsive Efficiency ◽  
Fish Locomotion ◽  
Pectoral Fins ◽  
Flow Features ◽  
Edge Vortex ◽  
Manta Ray

Recent advancement of bio-inspired underwater vehicles has led to a growing interest in understanding the fluid mechanics of fish locomotion, which involves complex interaction between the deforming structure and its surrounding fluid. Unlike most natural swimmers that undulate their body and caudal fin, manta rays employ an oscillatory mode by flapping their large, flattened pectoral fins to swim forward. Such a lift-based mode can achieve a substantially high propulsive efficiency, which is beneficial to long-distance swimming. In this study, numerical simulations are carried out on a realistic manta ray model to investigate the effect of pectoral fin kinematics on the propulsive performance and flow structure. A traveling wave model, which relates a local deflection angle to radial and azimuthal wavelengths, is applied to generate the motion of the pectoral fins. Hydrodynamic forces and propulsive efficiency are reported for systematically varying kinematic parameters such as wave amplitude and wavelengths. Key flow features, including a leading edge vortex (LEV) that forms close to the tip of each pectoral fin, and a wake consisting of interconnected vortex rings, are identified. In addition, how different fin motions alter the LEV behavior and hence affect the thrust and efficiency is illustrated.

scholarly journals Influence of Thickness Variation on the Flapping Performance of Symmetric NACA Airfoils in Plunging Motion

2010 ◽  
Vol 2010 ◽  
pp. 1-19 ◽  
Author(s):  
Liangyu Zhao ◽  
Shuxing Yang
Keyword(s):  
Lift Coefficient ◽  
Parametric Method ◽  
Leading Edge ◽  
Thickness Variation ◽  
Thrust Coefficient ◽  
Propulsive Efficiency ◽  
Maximum Thickness ◽  
Class Function ◽  
Edge Vortex ◽  
The Impact

In order to investigate the impact of airfoil thickness on flapping performance, the unsteady flow fields of a family of airfoils from an NACA0002 airfoil to an NACA0020 airfoil in a pure plunging motion and a series of altered NACA0012 airfoils in a pure plunging motion were simulated using computational fluid dynamics techniques. The “class function/shape function transformation“ parametric method was employed to decide the coordinates of these altered NACA0012 airfoils. Under specified plunging kinematics, it is observed that the increase of an airfoil thickness can reduce the leading edge vortex (LEV) in strength and delay the LEV shedding. The increase of the maximum thickness can enhance the time-averaged thrust coefficient and the propulsive efficiency without lift reduction. As the maximum thickness location moves towards the leading edge, the airfoil obtains a larger time-averaged thrust coefficient and a higher propulsive efficiency without changing the lift coefficient.

Wake Structures and Effect of Hydrofoil Shapes in Efficient Flapping Propulsion

2021 ◽  
Author(s):  
John Kelly ◽  
Pan Han ◽  
Haibo Dong ◽  
Tyler Van Buren
Keyword(s):  
Shape Change ◽  
Leading Edge ◽  
Chord Length ◽  
Immersed Boundary ◽  
Shape Transformation ◽  
Propulsive Efficiency ◽  
Favorable Pressure Gradient ◽  
Edge Vortex ◽  
And Performance ◽  
Numerical Solver

Abstract In this work, direct numerical simulation (DNS) is used to investigate how airfoil shape affects wake structure and performance during a pitching-heaving motion. First, a class-shape transformation (CST) method is used to generate airfoil shapes. CST coefficients are then varied in a parametric study to create geometries that are simulated in a pitching and heaving motion via an immersed boundary method-based numerical solver. The results show that most coefficients have little effect on the propulsive efficiency, but the second coefficient does have a very large effect. Looking at the CST basis functions shows that the effect of this coefficient is concentrated near the 25% mark of the foils chord length. By observing the thrust force and hydrodynamic power through a period of motion it is shown that the effect of the foil shape change is realized near the middle of each flapping motion. Through further inspection of the wake structures, we conclude that this is due to the leading-edge vortex attaching better to the foil shapes with a larger thickness around 25% of the chord length. This is verified by the pressure contours, which show a lower pressure along the leading edge of the better performing foils. The more favorable pressure gradient generated allows for higher efficiency motion.

Study of Pressure Shock Caused by a Vortex Ring Separated From a Vortex Rope in a Draft Tube Model

2017 ◽  
Vol 139 (8) ◽  
Author(s):  
S. G. Skripkin ◽  
M. A. Tsoy ◽  
P. A. Kuibin ◽  
S. I. Shtork
Keyword(s):  
Vortex Ring ◽  
High Speed ◽  
Draft Tube ◽  
Tube Wall ◽  
Quantitative Information ◽  
Tube Model ◽  
Vortex Rope ◽  
Swirl Generator ◽  
Vortex Ring Formation ◽  
Turbine Runner

Operating hydraulic turbines under part- or over-load conditions leads to the development of the precessing vortex rope downstream of the turbine runner. In a regime close to the best efficiency point (BEP), the vortex rope is very unstable because of the low residual swirl of the flow. However, strong pressure pulsations have been detected in the regime. These oscillations can be caused by self-merging and reconnection of a vortex helix with the formation of a vortex ring. The vortex ring moves along the wall of the draft tube and generates a sharp pressure pulse that is registered by pressure transducer. This phenomenon was investigated on a simplified draft tube model using a swirl generator consisting of a stationary swirler and a freely rotating runner. The experiments were performed at Reynolds number (Re) = 105. The measurements involved a high-speed visualization technique synchronized with pressure measurements on the draft tube wall, which enables an analysis of the key stages of vortex ring formation by comparing it with the pressure on the draft tube wall. Quantitative information regarding the average velocity distribution was obtained via the laser Doppler anemometer (LDA) technique.

Effect of axial skewed slot casing treatment in a transonic fan

2016 ◽  
Vol 231 (14) ◽  
pp. 2646-2653 ◽  
Author(s):  
Hossein Khaleghi
Keyword(s):  
High Speed ◽  
Leading Edge ◽  
Axial Fan ◽  
Lower Mass ◽  
Flow Rates ◽  
Casing Treatment ◽  
Mass Flow Rates ◽  
Edge Vortex ◽  
Upstream Part ◽  
Transonic Fan

This paper reports on a time-accurate numerical investigation of axial-skewed slot casing treatment in a high-speed axial fan. Twenty-two axial and radial skewed slots are placed over the casing of the rotor and choke to stall unsteady computations are conducted. Results show that endwall fluid is absorbed by the slots from the downstream part of the blade passage and is injected to the upstream part with a swirl contrary to the blade rotation. This gives the injected fluid a great circumferential velocity component in the relative frame of reference. The shock is, hence, pushed toward the trailing-edge plane and the pressure difference between the pressure and suction surfaces is reduced. Consequently, the occurrence of the leading-edge vortex spillage, which is believed to be the key to stall initiation for the current rotor, is postponed to lower mass flow rates.

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.

Experimental and Numerical Study on Flapping Wing Kinematics and Aerodynamics of Coleoptera

2006 ◽  
Vol 326-328 ◽  
pp. 175-178 ◽  
Author(s):  
Saputra ◽  
Do Young Byun ◽  
Yung Hwan Byun ◽  
Hoon Cheol Park
Keyword(s):  
Cross Section ◽  
High Speed ◽  
Numerical Study ◽  
Leading Edge ◽  
Aerodynamic Performance ◽  
Wing Kinematics ◽  
Wing Motion ◽  
Edge Vortex ◽  
Flapping Mechanism ◽  
Aerodynamic Simulation

In this study we have experimentally and numerically analyzed the flapping mechanism and wing kinematics of coleoptera (Propylea japonica Thunberg). Using digital high speed camera, we captured the continuous wing kinematics and visualized the flight motion of the free-flying coleoptera. The experimental visualization shows that the elytra flapped concurrently with the main wing both in the downstroke and upstroke motions. In order to define the wing kinematics of coleoptera, the displacement of a wing cross section (50% span-wise) was measured for each sequence of the wing motion. Using these data, the flight motion of coleoptera was numerically simulated to investigate the aerodynamic performance. The computational aerodynamic simulation shows that leading edge vortex shedding plays a key role in generating lift to keep the insect aloft.

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.

Effect of chordwise deformation on propulsive performance of flapping wings in forward flight

2020 ◽  
Vol 125 (1284) ◽  
pp. 430-451
Author(s):  
T. Lin ◽  
W. Xia ◽  
S. Hu
Keyword(s):  
Energy Dissipation ◽  
Strong Dependence ◽  
Leading Edge ◽  
Flapping Wing ◽  
Phase Lag ◽  
Thrust Coefficient ◽  
Propulsive Efficiency ◽  
Leading Edge Vortex ◽  
Propulsive Performance ◽  
Edge Vortex

ABSTRACTLack of flexibility limits the performance enhancement of man-made flapping wing Micro Air Vehicles (MAVs). Active chordwise deformation (bending) is introduced into the flapping wing model at low Reynolds number of Re = 200 in the present study. The lattice Boltzmann method with immersed boundary is adopted in the numerical simulation. The effects of the bending amplitude, bending frequency and phase lag between bending and flapping on the propulsive performance are analysed. The numerical results show that all the chordwise deformation parameters including the bending amplitude, bending frequency and phase lag have a great influence on the flow field, Leading-Edge Vortex (LEV), Trailing-Edge Vortex (TEV) and previous Leading-Edge Vortex (pLEV) of the deformable flapping wing, which leads to the variation of the propulsive performance. With decreasing bending amplitude and increasing bending frequency, both the thrust and energy dissipation coefficients increase. The highest thrust coefficient and highest energy dissipation coefficient occur at a phase lag of 180°. On the other hand, strong dependence of the propulsive efficiency on the vortex tangle is found. The highest propulsive efficiency is obtained for the present model at a dimensionless bending amplitude of 0.2, bending frequency of 0.7Hz, and phase lag of 0°.

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