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.

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.

Secondary instability and subcritical transition of the leading-edge boundary layer

2016 ◽  
Vol 792 ◽  
pp. 682-711 ◽  
Author(s):  
Michael O. John ◽  
Dominik Obrist ◽  
Leonhard Kleiser
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
High Speed ◽  
Three Dimensional ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Secondary Instability ◽  
Bypass Transition ◽  
Wall Suction ◽  
Transition Mechanism

The leading-edge boundary layer (LEBL) in the front part of swept airplane wings is prone to three-dimensional subcritical instability, which may lead to bypass transition. The resulting increase of airplane drag and fuel consumption implies a negative environmental impact. In the present paper, we present a temporal biglobal secondary stability analysis (SSA) and direct numerical simulations (DNS) of this flow to investigate a subcritical transition mechanism. The LEBL is modelled by the swept Hiemenz boundary layer (SHBL), with and without wall suction. We introduce a pair of steady, counter-rotating, streamwise vortices next to the attachment line as a generic primary disturbance. This generates a high-speed streak, which evolves slowly in the streamwise direction. The SSA predicts that this flow is unstable to secondary, time-dependent perturbations. We report the upper branch of the secondary neutral curve and describe numerous eigenmodes located inside the shear layers surrounding the primary high-speed streak and the vortices. We find secondary flow instability at Reynolds numbers as low as$Re\approx 175$, i.e. far below the linear critical Reynolds number$Re_{crit}\approx 583$of the SHBL. This secondary modal instability is confirmed by our three-dimensional DNS. Furthermore, these simulations show that the modes may grow until nonlinear processes lead to breakdown to turbulent flow for Reynolds numbers above$Re_{tr}\approx 250$. The three-dimensional mode shapes, growth rates, and the frequency dependence of the secondary eigenmodes found by SSA and the DNS results are in close agreement with each other. The transition Reynolds number$Re_{tr}\approx 250$at zero suction and its increase with wall suction closely coincide with experimental and numerical results from the literature. We conclude that the secondary instability and the transition scenario presented in this paper may serve as a possible explanation for the well-known subcritical transition observed in the leading-edge boundary layer.

scholarly journals Schlieren photography on freely flying hawkmoth

2018 ◽  
Vol 14 (5) ◽  
pp. 20180198 ◽  
Author(s):  
Yun Liu ◽  
Jesse Roll ◽  
Stephen Van Kooten ◽  
Xinyan Deng
Keyword(s):  
Aerodynamic Force ◽  
Leading Edge ◽  
Vortical Flow ◽  
Natural Setting ◽  
Optical Flow Method ◽  
Flying Insects ◽  
Flow Features ◽  
Potential Applications ◽  
Edge Vortex ◽  
Schlieren Photography

The aerodynamic force on flying insects results from the vortical flow structures that vary both spatially and temporally throughout flight. Due to these complexities and the inherent difficulties in studying flying insects in a natural setting, a complete picture of the vortical flow has been difficult to obtain experimentally. In this paper, Schlieren , a widely used technique for highspeed flow visualization, was adapted to capture the vortex structures around freely flying hawkmoth ( Manduca ). Flow features such as leading-edge vortex, trailing-edge vortex, as well as the full vortex system in the wake were visualized directly. Quantification of the flow from the Schlieren images was then obtained by applying a physics-based optical flow method, extending the potential applications of the method to further studies of flying insects.

The leading-edge vortex and aerodynamics of insect-based flapping-wing micro air vehicles

2009 ◽  
Vol 113 (1142) ◽  
pp. 253-262 ◽  
Author(s):  
P. C. Wilkins ◽  
K. Knowles
Keyword(s):  
Entire Range ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Micro Air Vehicles ◽  
Reynolds Numbers ◽  
Flapping Wing ◽  
Computational Method ◽  
Leading Edge Vortex ◽  
Air Vehicle ◽  
Edge Vortex

AbstractThe aerodynamics of insect-like flapping are dominated by the production of a large, stable, and lift-enhancing leading-edge vortex (LEV) above the wing. In this paper the phenomenology behind the LEV is explored, the reasons for its stability are investigated, and the effects on the LEV of changing Reynolds number or angle-of-attack are studied. A predominantly-computational method has been used, validated against both existing and new experimental data. It is concluded that the LEV is stable over the entire range of Reynolds numbers investigated here and that changes in angle-of-attack do not affect the LEV’s stability. The primary motivation of the current work is to ascertain whether insect-like flapping can be successfully ‘scaled up’ to produce a flapping-wing micro air vehicle (FMAV) and the results presented here suggest that this should be the case.

Velocity distribution around a sphere descending in a linearly stratified fluid

2017 ◽  
Vol 826 ◽  
pp. 759-780 ◽  
Author(s):  
Shinya Okino ◽  
Shinsaku Akiyama ◽  
Hideshi Hanazaki
Keyword(s):  
Boundary Layer ◽  
Velocity Distribution ◽  
High Speed ◽  
Particle Image ◽  
Maximum Velocity ◽  
Reynolds Numbers ◽  
Stratified Fluid ◽  
Velocity Variation ◽  
Image Velocimetry ◽  
Wave Patterns

The flow around a sphere descending at constant speed in a salt-stratified fluid is observed by particle image velocimetry. A unique characteristic of this flow is the appearance of a thin and high-speed rear jet whose maximum velocity can reach more than five times the sphere velocity. In this study we have investigated how the velocity distributions, especially those in the jet and in the boundary layer of the sphere, vary when the Froude number $Fr(=W^{\ast }/N^{\ast }a^{\ast })$ or the Reynolds number $Re(=W^{\ast }(2a^{\ast })/\unicode[STIX]{x1D708}^{\ast })$ ($W^{\ast }$: vertical velocity of the sphere, $N^{\ast }$: Brunt–Väisälä frequency, $a^{\ast }$: radius of the sphere, $\unicode[STIX]{x1D708}^{\ast }$: kinematic viscosity of the fluid) is changed. The results show that the radius of the jet and the thickness of the boundary layer are comparable, and they decrease for smaller Froude numbers and larger Reynolds numbers. Both of them are estimated at moderate Reynolds numbers by the primitive length scale of the stratified fluid ($l_{\unicode[STIX]{x1D708}}^{\ast }=\sqrt{\unicode[STIX]{x1D708}^{\ast }/N^{\ast }}$), or in non-dimensional form by $l_{\unicode[STIX]{x1D708}}^{\ast }/2a^{\ast }=(Fr/2Re)^{1/2}$. The overall velocity distribution in the lee of the sphere is measured to identify the internal wave patterns and their effect on the velocity variation along the jet. Corresponding numerical simulation results using the axisymmetry assumption are in agreement with the experimental results.

Wake Behavior Around Flapping Wings of Model Hawkmoth Moving Sideways

2019 ◽  
Author(s):  
Jong-Seob Han ◽  
Jae-Hung Han
Keyword(s):  
Particle Image ◽  
Leading Edge ◽  
Aerodynamic Characteristics ◽  
Digital Particle Image Velocimetry ◽  
Flapping Wings ◽  
Windward Side ◽  
Leeward Side ◽  
Image Velocimetry ◽  
Wake Interaction ◽  
Edge Vortex

Abstract This study investigated nearwake behaviors around flapping wings moving sideways. A dynamically scaled-up flapping manipulator was installed on a servo-driven towing carriage to give the sideways movement. In the single wing configuration, the wing in the windward side did not encounter any noticeable effects on the aerodynamic characteristics. The wing in the leeward side, on the other hand, experienced a substantial lift augmentation. We found a stretched leading-edge vortex (LEV) on the wing in the leeward side, implying the additional feeding flux into the LEV. In this case, the moving sideways gave a continuous lateral wind, which became the source to maintain the lift augmentation with the less downward component. We also found that the moving sideways rather intensified the interaction between the wake of the wing in the windward side and the contralateral wing, i.e., the wing-wake interaction. Accordingly, the lift augmentation on the wing in the leeward side practically disappeared by the wing-wake interaction. A digital particle image velocimetry for nearwake behaviors found the less developed trailing-edge shear layer and wingroot vortex traces. This implied that the massive downwash induced by the wing in the windward side was the main source to neutralize the lift augmentation on the contralateral wing.

Experimental Investigation of Blood Cells Flowing Through Microscale Geometries Using MicroPIV

2012 ◽  
Author(s):  
Vishwanath Somashekar ◽  
Michael G. Olsen ◽  
K. B. Chandran ◽  
H. S. Udaykumar
Keyword(s):  
Particle Image Velocimetry ◽  
Platelet Activation ◽  
Blood Cells ◽  
Particle Image ◽  
Mechanical Heart Valve ◽  
Reynolds Numbers ◽  
High Shear ◽  
Endothelial Layer ◽  
Micro Particle Image Velocimetry ◽  
Image Velocimetry

The advances made in the field of cardiovascular prostheses have proved invaluable in saving human lives. However, implanting such a device may cause unwanted results like thrombosis, the formation of blood clots inside blood vessels. This formation of thrombi can affect the flow of blood, which if left untreated may result in strokes. As the blood moves through various arteries and veins, the platelets move toward the periphery and the red blood cells (RBC) are more concentrated near the center. This process is called margination and has been shown by Aarts et al.[1]. The platelets in essence are policing the endothelial layer, and with any change in the endothelial layer, say as a result of injury, the platelets get activated, which in turn starts a domino effect eventually resulting in the formation of a clot to stop the bleeding. These platelets can also get activated due to their presence in regions of high shear as is the case when the blood is flowing through narrow constrictions (for example, when a mechanical heart valve is about to close). This phenomenon is referred to as Shear Induced Platelet Activation (SIPA)[2]. The goal of this research is to study the effect of constricted geometries, high shear rates and erythrocyte-platelet interactions on platelet activation and aggregate formation, events that are critical in the initiation of thrombosis. In order to understand SIPA, one must first obtain a detailed flow in these constricted geometries. Numerous studies have been performed to obtain the flow fields of blood flowing through microchannels [3, 4]. However, the Reynolds numbers based on the characteristic length of the microchannel were in the O (1). It is worth noting that for such laminar flows confocal particle image velocimetry can be successfully applied. In this present study, the Reynolds numbers were in the O (100), rendering confocal mPIV impractical and making Micro Particle Image Velocimetry (mPIV) a clear choice.

Vortical feeding currents in nauplii of the calanoid copepod Eucalanus pileatus

2020 ◽  
Vol 638 ◽  
pp. 51-63 ◽  
Author(s):  
H Jiang ◽  
GA Paffenhöfer
Keyword(s):  
High Speed ◽  
Calanoid Copepod ◽  
Imaging System ◽  
Ventral Surface ◽  
Food Concentration ◽  
Core Flow ◽  
Micro Particle Image Velocimetry ◽  
Swimming Motion ◽  
Image Velocimetry ◽  
Beat Pattern

The goal of this study was to quantify feeding-current generation processes in mid to late nauplii and early copepodites of the calanoid copepod Eucalanus pileatus. Using a high-speed microscale imaging system (HSMIS) to conduct both microvideography and micro-particle image velocimetry (µPIV), free-swimming nauplii of E. pileatus were shown to use a novel ‘double draw-and-cut’ continuous appendage beat pattern, which is nonreciprocal, to generate a vortical feeding current at a Reynolds number of ~0.8. The feeding current consists of a core flow towards the ventral surface and 2 laterally flanking viscous vortices reinforcing the core flow. This feeding current is spatially limited with an r-3 decay, potentially reducing predation by rheotactic predators. The feeding current displaces water at ~1.0 × 106 naupliar body volumes per day towards the mouthpart zone. This would result in a clearance rate providing sufficient food at a relatively high environmental food concentration. HSMIS videos revealed that E. pileatus nauplii combine their feeding current and swimming motion to displace algae towards their mouth for capture, and can react to an incoming alga at a 300-500 µm distance away from the nearest naupliar setae, indicating remote detection presumably via chemoreception. The r-3-decay naupliar feeding current is suggested to enhance chemoreception by more effectively elongating the algal phycosphere towards the nauplius. Compared with nauplii, E. pileatus early copepodites, being larger in size and negatively buoyant, beat appendages in a more complex, intermittent pattern to generate an r-1-decay feeding current for displacing more water, indicating a trade-off among feeding, predator avoidance, and alga perception.

Sign in / Sign up

Export Citation Format

Share Document