Hydrodynamics of swimming in stingrays: numerical simulations and the role of the leading-edge vortex

2016 ◽  
Vol 788 ◽  
pp. 407-443 ◽  
Author(s):  
R. G. Bottom II ◽  
I. Borazjani ◽  
E. L. Blevins ◽  
G. V. Lauder
Keyword(s):  
Three Dimensional ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Low Pressure ◽  
Body Motion ◽  
Vortical Structures ◽  
Leading Edge Vortex ◽  
Large Eddy ◽  
Pressure Region ◽  
Edge Vortex

Stingrays, in contrast with many other aquatic animals, have flattened disk-shaped bodies with expanded pectoral ‘wings’, which are used for locomotion in water. To discover the key features of stingray locomotion, large-eddy simulations of a self-propelled stingray, modelled closely after the freshwater stingray, Potamotrygon orbignyi, are performed. The stingray’s body motion was prescribed based on three-dimensional experimental measurement of wing and body kinematics in live stingrays at two different swimming speeds of 1.5 and $2.5L~\text{s}^{-1}$ ($L$ is the disk length of the stingray). The swimming speeds predicted by the self-propelled simulations were within 12 % of the nominal swimming speeds in the experiments. It was found that the fast-swimming stingray (Reynolds number $Re=23\,000$ and Strouhal number $St=0.27$) is approximately 12 % more efficient than the slow-swimming one ($Re=13\,500$, $St=0.34$). This is related to the wake of the fast- and slow-swimming stingrays, which was visualized along with the pressure on the stingray’s body. A horseshoe vortex was discovered to be present at the anterior margin of the stingray, creating a low-pressure region that enhances thrust for both fast and slow swimming speeds. Furthermore, it was found that a leading-edge vortex (LEV) on the pectoral disk of swimming stingrays generates a low-pressure region in the fast-swimming stingray, whereas the low- and high-pressure regions in the slow-swimming one are in the back half of the wing and not close to any vortical structures. The undulatory motion creates thrust by accelerating the adjacent fluid (the added-mass mechanism), which is maximized in the back of the wing because of higher undulations and velocities in the back. However, the thrust enhancement by the LEV occurs in the front portion of the wing. By computing the forces on the front half and the back half of the wing, it was found that the contribution of the back half of the wing to thrust in a slow-swimming stingray is several-fold higher than in the fast-swimming one. This indicates that the LEV enhances thrust in fast-swimming stingrays and improves the efficiency of swimming.

scholarly journals Impact of Leading Edge Roughness in Cavitation Simulations around a Twisted Foil

Fluids ◽  
2020 ◽  
Vol 5 (4) ◽  
pp. 243
Author(s):  
Abolfazl Asnaghi ◽  
Rickard E. Bensow
Keyword(s):  
Three Dimensional ◽  
Leading Edge ◽  
Flow Structures ◽  
Vortical Structures ◽  
Vorticity Distribution ◽  
Eddy Simulation ◽  
Roughness Elements ◽  
Edge Roughness ◽  
Large Eddy ◽  
Implicit Large Eddy Simulation

The simulation of fully turbulent, three-dimensional, cavitating flow over Delft twisted foil is conducted by an implicit large eddy simulation (LES) approach in both smooth and tripped conditions, the latter by including leading-edge roughness. The analysis investigates the importance of representing the roughness elements on the flow structures in the cavitation prediction. The results include detailed comparisons of cavitation pattern, vorticity distribution, and force predictions with the experimental measurements. It is noted that the presence of roughness generates very small cavitating vortical structures which interact with the main sheet cavity developing over the foil to later form a cloud cavity. Very similar to the experimental observation, these interactions create a streaky sheet cavity interface which cannot be captured in the smooth condition, influencing both the richness of structures in the detached cloudy cavitation as well as the extent and transport of vapour. It is further found to have a direct impact on the pressure distribution, especially in the mid-chord region where the shed cloud cavity collapses.

scholarly journals The leading-edge vortex on a rotating wing changes markedly beyond a certain central body size

2018 ◽  
Vol 5 (7) ◽  
pp. 172197 ◽  
Author(s):  
Shantanu S. Bhat ◽  
Jisheng Zhao ◽  
John Sheridan ◽  
Kerry Hourigan ◽  
Mark C. Thompson
Keyword(s):  
Reynolds Number ◽  
Body Size ◽  
Central Body ◽  
Three Dimensional ◽  
Leading Edge ◽  
Particle Image Velocimetry Technique ◽  
Leading Edge Vortex ◽  
Rapid Acquisition ◽  
Edge Vortex ◽  
Rotating Wing

Stable attachment of a leading-edge vortex (LEV) plays a key role in generating the high lift on rotating wings with a central body. The central body size can affect the LEV structure broadly in two ways. First, an overall change in the size changes the Reynolds number, which is known to have an influence on the LEV structure. Second, it may affect the Coriolis acceleration acting across the wing, depending on the wing-offset from the axis of rotation. To investigate this, the effects of Reynolds number and the wing-offset are independently studied for a rotating wing. The three-dimensional LEV structure is mapped using a scanning particle image velocimetry technique. The rapid acquisition of images and their correlation are carefully validated. The results presented in this paper show that the LEV structure changes mainly with the Reynolds number. The LEV-split is found to be only minimally affected by changing the central body radius in the range of small offsets, which interestingly includes the range for most insects. However, beyond this small offset range, the LEV-split is found to change dramatically.

An Explanation for Flow Features of Spike-Type Stall Inception in an Axial Compressor Rotor

2012 ◽  
Author(s):  
Kazutoyo Yamada ◽  
Hiroaki Kikuta ◽  
Ken-ichiro Iwakiri ◽  
Masato Furukawa ◽  
Satoshi Gunjishima
Keyword(s):  
Flow Structure ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Leading Edge ◽  
Low Pressure ◽  
Stall Inception ◽  
Compressor Rotor ◽  
Pressure Region ◽  
Casing Pressure ◽  
Edge Separation

The unsteady behavior and three-dimensional flow structure of spike-type stall inception in an axial compressor rotor have been investigated by experimental and numerical analyses. Previous studies have revealed that the test compressor falls into a mild stall after emergence of a spike, in which multiple stall cells, each consisting of a tornado-like vortex, are rotating. However, the flow mechanism from the spike onset to the mild stall remains unexplained. The purpose of this study is to describe the flow mechanism of a spike stall inception in a compressor. In order to capture the transient phenomena of spike-type stall inception experimentally, an instantaneous casing pressure field measurement technique was developed, in which 30 pressure transducers measure an instantaneous casing pressure distribution inside the passage for one blade pitch at a rate of 25 samplings per blade passing period. This technique was applied to obtain the unsteady and transient pressure fields on the casing wall during the inception process of the spike stall. In addition, the details of the three-dimensional flow structure at the spike stall inception have been analyzed by a numerical approach using the detached-eddy simulation (DES). The instantaneous casing pressure field measurement results at the stall inception show that a low-pressure region starts traveling near the leading edge in the circumferential direction just after the spiky wave was detected in the casing wall pressure trace measured near the rotor leading edge. The DES results reveal the vortical flow structure behind the low-pressure region on the casing wall at the stall inception, showing that the low-pressure region is caused by a tornado-like separation vortex resulting from a leading-edge separation near the rotor tip. A leading-edge separation occurs near the tip at the onset of the spike stall and grows to form the tornado-like vortex connecting the blade suction surface and the casing wall. The casing-side leg of the tornado-like vortex generating the low-pressure region circumferentially moves around the leading-edge line. When the vortex grows large enough to interact with the leading edge of the next blade, the leading-edge separation begins to propagate, and then, the compressor falls into a stall with decreasing performance.

Three-Dimensional Solution of Flows over Wings with Leading-Edge Vortex Separation

AIAA Journal ◽  
1976 ◽  
Vol 14 (4) ◽  
pp. 519-525 ◽  
Author(s):  
James A. Weber ◽  
Guenter W. Brune ◽  
Forrester T. Johnson ◽  
Paul Lu ◽  
Paul E. Rubbert
Keyword(s):  
Three Dimensional ◽  
Leading Edge ◽  
Dimensional Solution ◽  
Leading Edge Vortex ◽  
Vortex Separation ◽  
Edge Vortex

Characterization of a Three-Dimensional Leading-Edge Separation Bubble on Swept, Low Aspect-Ratio Propeller Blades

2017 ◽  
Author(s):  
Ye-Bonne Koyama Maldonado ◽  
Gregory Delattre ◽  
Cedric Illoul ◽  
Clement Dejeu ◽  
Laurent Jacquin
Keyword(s):  
Delta Wing ◽  
Separation Bubble ◽  
Three Dimensional ◽  
Leading Edge ◽  
Time Resolved ◽  
Leading Edge Vortex ◽  
Wall Structures ◽  
Edge Vortex ◽  
Propeller Blades ◽  
Leading Edge Vortices

Leading-edge vortex flows are often present on propeller blades at take-off, however, their characteristics and aerodynamic impact are still not fully understood. An experimental investigation using Time Resolved Particle Image Velocimetry (TR-PIV) has been performed on a model blade in order to classify this flow with respect to both delta wing leading-edge vortices and the low Reynolds number studies regarding leading-edge vortices on rotating blades. A numerical calculation of the experimental setup has been performed in order to assess usual numerical methods for propeller performance prediction against TR-PIV results. Similar characteristics were found with non slender delta wing vortices at low incidence, which hints that the leading-edge vortex flow may generate vortex lift. The influence of rotation on the characteristics of the leading-edge vortex is compared to that of the pressure gradient caused by the circulation distribution. A discussion on the quality of the PIV reconstruction for close-wall structures is provided.

scholarly journals The three–dimensional leading–edge vortex of a ‘hovering’ model hawkmoth

1997 ◽  
Vol 352 (1351) ◽  
pp. 329-340 ◽  
Author(s):  
Coen van den Berg ◽  
Charles P. Ellington
Keyword(s):  
Wing Length ◽  
Three Dimensional ◽  
Axial Flow ◽  
Leading Edge ◽  
Tip Vortex ◽  
Flow Visualisation ◽  
High Lift ◽  
Leading Edge Vortex ◽  
Edge Vortex ◽  
Wing Chord

Recent flow visualisation experiments with the hawkmoth, Manduca sexta , revealed small but clear leading–edge vortex and a pronounced three–dimensional flow. Details of this flow pattern were studied with a scaled–up, robotic insect (‘the flapper’) that accurately mimicked the wing movements of a hovering hawkmoth. Smoke released from the leading edge of the flapper wing confirmed the existence of a small, strong and stable leading–edge vortex, increasing in size from wingbase to wingtip. Between 25 and 75 % of the wing length, its diameter increased approximately from 10 to 50 % of the wing chord. The leading–edge vortex had a strong axial flow veolocity, which stabilized it and reduced its diamater. The vortex separated from the wing at approximately 75 % of the wing length and thus fed vorticity into a large, tangled tip vortex. If the circulation of the leading–edge vortex were fully used for lift generation, it could support up to two–thirds of the hawkmoth's weight during the downstroke. The growth of this circulation with time and spanwise position clearly identify dynamic stall as the unsteady aerodynamic mechanism responsible for high lift production by hovering hawkmoths and possibly also by many other insect species.

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