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.

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.

Vortex dynamics and hydrodynamic performance enhancement mechanism in batoid fish oscillatory swimming

2021 ◽  
Vol 930 ◽  
Author(s):  
Dong Zhang ◽  
Qiao-Gao Huang ◽  
Guang Pan ◽  
Li-Ming Yang ◽  
Wei-Xi Huang
Keyword(s):  
Vortex Dynamics ◽  
Performance Enhancement ◽  
Leading Edge ◽  
Biological Data ◽  
Tip Vortex ◽  
Hydrodynamic Performance ◽  
Immersed Boundary ◽  
Transformation Theory ◽  
Enhancement Mechanism ◽  
Edge Vortex

The effects of chordwise deformation and the half-amplitude asymmetry on the hydrodynamic performance and vortex dynamics of batoid fish have been numerically investigated, in which the two parameters were represented by the wavenumber ( $W$ ) and the ratio of the half-amplitude above the longitudinal axis to that below ( $HAR$ ). Fin kinematics were prescribed based on biological data. Simulations were conducted using the immersed boundary method. It was found that moderate chordwise deformation enhances the thrust, saves the power and increases the efficiency. A large $HAR$ can also increase thrust performance. By using the derivative-moment transformation theory at several subdomains to capture the local vortical structures and a force decomposition, it was shown that, at high Strouhal numbers ( $St$ ), the tip vortex is the main source of thrust, whereas the leading-edge vortex (LEV) and trailing-edge vortex weaken the thrust generation. However, at lower $St$ , the LEV would enhance the thrust. The least deformation ( $W=0$ ) leads to the largest effective angle of attack, and thus the strongest vortices. However, moderate deformation ( $W=0.4$ ) has an optimal balance between the performance enhancement and the opposite effect of different local structures. The performance enhancement of $HAR$ was also due to the increase of the vortical contributions. This work provides a new insight into the role of vortices and the force enhancement mechanism in aquatic swimming.

Hydrodynamics of flexible fins propelled in tandem, diagonal, triangular and diamond configurations

2018 ◽  
Vol 840 ◽  
pp. 154-189 ◽  
Author(s):  
Sung Goon Park ◽  
Hyung Jin Sung
Keyword(s):  
Immersed Boundary Method ◽  
Leading Edge ◽  
Input Power ◽  
Immersed Boundary ◽  
Diamond Formation ◽  
Propulsive Efficiency ◽  
Fish Schools ◽  
Fluid Environment ◽  
Dimensional Simulation ◽  
Surrounding Fluid

A fish may gain hydrodynamic benefits from being a member of a school. Inspired by fish schools, a two-dimensional simulation was performed for flexible fins propelled in tandem, diagonal, triangular and diamond configurations. The flow-mediated interactions between the flexible fins were analysed by using an immersed boundary method. A transverse heaving motion was prescribed on the leading edge of each fin, and other posterior parts passively adapted to the surrounding fluid as a result of the fluid–flexible-body interaction. The flexible fins were allowed to actively adjust their relative positions in the horizontal direction. The four basic stable configurations are spontaneously formed and self-sustained purely by the vortex–vortex and vortex–body interactions. The hydrodynamic benefits depend greatly on the local positions of the members. For the same heaving motion prescribed on the leading edge, the input power of the following fin in the stable tandem and diagonal configurations is lower by 14 % and 6 %, respectively, than that of the leading fin. The following fin in the diagonal formation can keep pace with the leading fin even for reduced heaving amplitudes because of the help of the leader via their shared fluid environment, where its required input power is reduced by 21 %. The heaving amplitudes of the trailing fins are reduced to optimize the propulsive efficiency, and the average efficiencies in the triangular and diamond configurations increase by up to 14 % and 19 %, respectively, over that of the isolated swimmer. The propulsive efficiencies are enhanced by 22 % for the fins in the second row and by 36 % for the fin in the third row by decreasing the heaving amplitude in the diamond formation.

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.

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°.

scholarly journals Swimming and Flying in Nature—The Route Toward Applications: The Freeman Scholar Lecture

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Promode R. Bandyopadhyay
Keyword(s):  
Life Form ◽  
Leading Edge ◽  
Future Research ◽  
Science And Engineering ◽  
High Lift ◽  
The Status ◽  
Edge Vortex ◽  
The Subject ◽  
And Performance ◽  
And Control

Evolution is a slow but sure process of perfecting design to give a life-form a natural advantage in a competitive environment. The resulting complexity and performance are so sophisticated that, by and large, they are yet to be matched by man-made devices. They offer a vast array of design inspirations. The lessons from swimming and flying animals that are useful to fluids engineering devices are considered. The science and engineering of this subject—termed “biorobotics” here—are reviewed. The subject, being of dynamic objects, spans fluid dynamics, materials, and control, as well as their integration. The emphasis is on understanding the underlying science and design principles and applying them to transition to human usefulness rather than to conduct any biomimicry. First, the gaps between nature and man-made devices in terms of fluids engineering characteristics are quantitatively defined. To bridge these gaps, we then identify the underlying science principles in the production of unsteady high-lift that nature is boldly using, but that engineers have preferred to refrain from or have not conceived of. This review is primarily concerned with the leading-edge vortex phenomenon that is mainly responsible for unsteady high-lift. Next, design laws are determined. Several applications are discussed and the status of the closure of the gaps between nature and engineering is reviewed. Finally, recommendations for future research in unsteady fluids engineering are given.

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

scholarly journals Towards higher aerodynamic efficiency of propeller-driven aircraft with distributed propulsion

2021 ◽  
Author(s):  
Dennis Keller
Keyword(s):  
Performance Indicator ◽  
Leading Edge ◽  
Substantial Improvement ◽  
Initial Assessment ◽  
Local Flow ◽  
Propulsive Efficiency ◽  
Thrust Distribution ◽  
Distributed Propulsion ◽  
Wing Tip ◽  
Cruise Flight

AbstractThe scope of the present paper is to assess the potential of distributed propulsion for a regional aircraft regarding aero-propulsive efficiency. Several sensitivities such as the effect of wingtip propellers, thrust distribution, and shape modifications are investigated based on a configuration with 12 propulsors. Furthermore, an initial assessment of the high-lift performance is undertaken in order to estimate potential wing sizing effects. The performance of the main wing and the propellers are thereby equally considered with the required power being the overall performance indicator. The results indicate that distributed propulsion is not necessarily beneficial regarding the aero-propulsive efficiency in cruise flight. However, the use of wing tip propellers, optimization of the thrust distribution, and wing resizing effects lead to a reduction in required propulsive power by $$-2.9$$ - 2.9 to $$-3.3\,\%$$ - 3.3 % compared to a configuration with two propulsors. Adapting the leading edge to the local flow conditions did not show any substantial improvement in cruise configuration to date.

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