scholarly journals An aeroelastic instability provides a possible basis for the transition from gliding to flapping flight

2013 ◽  
Vol 10 (80) ◽  
pp. 20120940 ◽  
Author(s):  
Oscar M. Curet ◽  
Sharon M. Swartz ◽  
Kenneth S. Breuer
Keyword(s):  
Lift Coefficient ◽  
Leading Edge ◽  
Flapping Flight ◽  
Fluid Forces ◽  
Low Wind Speed ◽  
Stiffness Properties ◽  
Edge Vortex ◽  
Lifting Surfaces ◽  
Drag Ratio ◽  
Lift To Drag Ratio

The morphology, kinematics and stiffness properties of lifting surfaces play a key role in the aerodynamic performance of vertebrate flight. These surfaces, as a result of their flexible nature, may move both actively, owing to muscle contraction, and passively, in reaction to fluid forces. However, the nature and implications of this fluid–structure interaction are not well understood. Here, we study passive flight (flight with no active wing actuation) and explore a physical mechanism that leads to the emergence of a natural flapping motion. We model a vertebrate wing with a compliant shoulder and the ability to camber with an idealized physical model consisting of a cantilevered flat plate with a hinged trailing flap. We find that at low wind speed the wing is stationary, but at a critical speed the wing spontaneously flaps. The lift coefficient is significantly enhanced once the wing starts to oscillate, although this increase in lift generation is accompanied by an increase in drag. Flow visualization suggests that a strong leading edge vortex attached to the wing during downstroke is the primary mechanism responsible for the enhanced lift. The flapping instability we observe suggests a possible scenario for an evolutionary transition from gliding to powered flapping flight in animals that possess compliant wings capable of passive camber. Although the flapping state is accompanied by a lower lift-to-drag ratio, the increased lifting capability it confers might have enabled increased body mass, improved foraging performance and/or flight at lower speeds, any of which might have been selectively advantageous.

Effects of leading-edge bevel angle on the aerodynamic forces of a non-slender 50° delta wing

2005 ◽  
Vol 109 (1098) ◽  
pp. 403-407 ◽  
Author(s):  
J. J. Wang ◽  
S. F. Lu
Keyword(s):  
Delta Wing ◽  
Lift Coefficient ◽  
Leading Edge ◽  
Relative Thickness ◽  
Aerodynamic Performances ◽  
Stall Angle ◽  
Drag Ratio ◽  
Low Speed Wind Tunnel ◽  
Lift To Drag Ratio ◽  
Blunt Leading Edge

Abstract The aerodynamic performances of a non-slender 50° delta wing with various leading-edge bevels were measured in a low speed wind tunnel. It is found that the delta wing with leading-edge bevelled leeward can improve the maximum lift coefficient and maximum lift to drag ratio, and the stall angle of the wing is also delayed. In comparison with the blunt leading-edge wing, the increment of maximum lift to drag ratio is 200%, 98% and 100% for the wings with relative thickness t/c = 2%, t/c = 6.7% and t/c = 10%, respectively.

Lift Augmentation between Passive and Active Vortex Generator

2016 ◽  
Vol 851 ◽  
pp. 532-537
Author(s):  
Nur Faraihan Zulkefli ◽  
Zulhilmy Sahwee ◽  
Nurhayati Mohd Nur ◽  
Muhamad Nor Ashraf Mohd Fazil ◽  
Muaz Mohd Shukri
Keyword(s):  
Reynolds Number ◽  
Lift Coefficient ◽  
Vortex Generator ◽  
Leading Edge ◽  
Plasma Actuator ◽  
Triangular Shape ◽  
Subsonic Wind Tunnel ◽  
Different Types ◽  
Drag Ratio ◽  
Lift To Drag Ratio

This study was conducted to investigate the performance of passive and active vortex generator on the wing’s flap. The triangular shape of passive vortex generator (VG) was developed and attached on the wing’s flap leading edge while the plasma actuator performed as active vortex generator. The test was carried out experimentally using subsonic wind tunnel with 300 angles extended flap. Three different types of turbulent flow; with Reynolds number 1.5 x105, 2.0 x105, and 2.6x105 were used to study the aerodynamics forces of airfoil with plasma actuator OFF. All Reynolds number used were below 1x106. The result indicated that airfoil with plasma actuator produced higher lift coefficient 12% and lift-to-drag ratio 5% compared to airfoil with passive vortex generator. The overall result showed that airfoil with plasma actuator produced better lift forces compared to passive vortex generator.

Numerical Investigation of Bionic Rudder With Leading-Edge Protuberances

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Hongtao Gao ◽  
Wencai Zhu
Keyword(s):  
Electron Microscopy ◽  
Lift Coefficient ◽  
Leading Edge ◽  
Hydrodynamic Performance ◽  
Spanwise Direction ◽  
Flow Mechanism ◽  
Suction Surface ◽  
Edge Profile ◽  
Drag Ratio ◽  
Lift To Drag Ratio

The duck's webbed feet are observed by using electron microscopy, and observations indicate that the edges of the webbed feet are the shape of protuberances. Therefore, the rudder with leading-edge protuberances is numerically studied in the present investigation. The rudder has a sinusoidal leading-edge profile along the spanwise direction. The hydrodynamic performance of rudder is analyzed under the influence of leading-edge protuberances. The present investigations are carried out at Re = 3.2 × 105 and 8 × 105. In the case of Re = 3.2 × 105, the curves of lift coefficient illustrate that the protuberant leading-edge scarcely affects the lift coefficient of bionic rudder. However, the drag coefficient of the bionic rudder is markedly lower than that of the unmodified rudder. Therefore, the lift-to-drag ratio of the bionic rudder is obviously higher than the unmodified rudder. In another case of Re = 8 × 105, the advantageous behavior of the bionic rudder with leading-edge protuberances is mainly performed in the post-stall regime. The flow mechanism of the significantly increased efficiency by the protuberant leading-edge is explored. It is obvious that the pairs of counter-rotating vortices are presented over the suction surface of bionic rudder, and therefore, the flow is more likely to adhere to the suction surface of bionic rudder.

Vortex development on pitching plates with lunate and truncate planforms

2013 ◽  
Vol 732 ◽  
pp. 332-344 ◽  
Author(s):  
Colin Hartloper ◽  
David E. Rival
Keyword(s):  
Vortex Formation ◽  
Three Dimensional ◽  
Leading Edge ◽  
Strongly Correlated ◽  
Near Wake ◽  
Relaxation Phase ◽  
Force Relaxation ◽  
Edge Vortex ◽  
Drag Ratio ◽  
Lift To Drag Ratio

AbstractThe three-dimensional flow field and instantaneous forces are measured on pitching rectangular, lunate and truncate planforms of aspect-ratio four. The leading-edge vortex on the rectangular planform is compressed as it grows, and subsequently forms an arch-shaped vortex. For the lunate and truncate planforms, which both have identical spanwise leading-edge curvature but differ in planform area, outboard-directed convection of vorticity, rather than vortex stretching, mitigates arch-vortex formation. The vortical near wake that is formed by the planforms with spanwise leading-edge curvature is found to be strongly correlated with a favourable lift-to-drag ratio during the force-relaxation phase.

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.

scholarly journals Aerodynamic and Vibration Characteristics of the Micro-Octocopter at Low Reynolds Number

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Xiaohua Zou ◽  
Mingsheng Ling ◽  
Wenzheng Zhai
Keyword(s):  
Reynolds Number ◽  
Load Capacity ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Aerodynamic Characteristics ◽  
Vibration Characteristics ◽  
Low Reynolds ◽  
Vibration Performance ◽  
Drag Ratio ◽  
Lift To Drag Ratio

With the development of flight technology, the need for stable aerodynamic and vibration performance of the aircraft in the civil and military fields has gradually increased. In this case, the requirements for aerodynamic and vibration characteristics of the aircraft have also been strengthened. The existing four-rotor aircraft carries limited airborne equipment and payload, while the current eight-rotor aircraft adopts a plane layout. The size of the propeller is generally fixed, including the load capacity. The upper and lower tower layout analyzed in this paper can effectively solve the problems of insufficient four-axis load and unstable aerodynamic and vibration performance of the existing eight-axis aircraft. This paper takes the miniature octorotor as the research object and studies the aerodynamic characteristics of the miniature octorotor at different low Reynolds numbers, different air pressures and thicknesses, and the lift coefficient and lift-to-drag ratio, as well as the vibration under different elastic moduli and air pressure characteristics. The research algorithm adopted in this paper is the numerical method of fluid-solid cohesion and the control equation of flow field analysis. The research results show that, with the increase in the Reynolds number within a certain range, the aerodynamic characteristics of the miniature octorotor gradually become better. When the elastic modulus is 2.5 E, the aircraft’s specific performance is that the lift increases, the critical angle of attack increases, the drag decreases, the lift-to-drag ratio increases significantly, and the angle of attack decreases. However, the transition position of the flow around the airfoil surface is getting closer to the leading edge, and its state is more likely to transition from laminar flow to turbulent flow. When the unidirectional carbon fiber-reinforced thickness is 0.2 mm and the thin arc-shaped airfoil with the convex structure has a uniform thickness of 2.5% and a uniform curvature of 4.5%, the aerodynamic and vibration characteristics of the octorotor aircraft are most beneficial to flight.

scholarly journals On the lift-optimal aspect ratio of a revolving wing at low Reynolds number

2018 ◽  
Vol 15 (143) ◽  
pp. 20170933 ◽  
Author(s):  
T. Jardin ◽  
T. Colonius
Keyword(s):  
Aspect Ratio ◽  
Lift Coefficient ◽  
Leading Edge ◽  
Rossby Number ◽  
Subsequent Work ◽  
High Lift ◽  
Low Aspect Ratio ◽  
Axis Of Rotation ◽  
Edge Vortex ◽  
Convergent Solution

Lentink & Dickinson (2009 J. Exp. Biol. 212 , 2705–2719. ( doi:10.1242/jeb.022269 )) showed that rotational acceleration stabilized the leading-edge vortex on revolving, low aspect ratio (AR) wings and hypothesized that a Rossby number of around 3, which is achieved during each half-stroke for a variety of hovering insects, seeds and birds, represents a convergent high-lift solution across a range of scales in nature. Subsequent work has verified that, in particular, the Coriolis acceleration plays a key role in LEV stabilization. Implicit in these results is that there exists an optimal AR for wings revolving about their root, because it is otherwise unclear why, apart from possible morphological reasons, the convergent solution would not occur for an even lower Rossby number. We perform direct numerical simulations of the flow past revolving wings where we vary the AR and Rossby numbers independently by displacing the wing root from the axis of rotation. We show that the optimal lift coefficient represents a compromise between competing trends with competing time scales where the coefficient of lift increases monotonically with AR, holding Rossby number constant, but decreases monotonically with Rossby number, when holding AR constant. For wings revolving about their root, this favours wings of AR between 3 and 4.

Optimal Design of Wind Turbines Using BIAS, A Method of Multipliers Code

1988 ◽  
Author(s):  
B. D. Vick ◽  
W. Wrigglesworth ◽  
L. B. Scott ◽  
K. M. Ragsdell
Keyword(s):  
Optimal Design ◽  
Rough Surface ◽  
Wind Turbines ◽  
Lift Coefficient ◽  
Power Coefficient ◽  
Method Of Multipliers ◽  
High Lift ◽  
Small Wind Turbines ◽  
Drag Ratio ◽  
Lift To Drag Ratio

Abstract A method has been developed and is demonstrated which determines the chord and twist distribution for a wind turbine with maximum power coefficient. Only small wind turbines (less than 10 kilowatts) are considered in this study, but the method could be used for larger wind turbines. Glauert determined a method for estimating the chord and twist distribution that will maximize the power coefficient if there is no drag. However, the method proposed here determines the chord and twist distribution which will maximize the power coefficient with the effect of drag included. Including drag in the analysis does not significantly affect the Glauert chord and twist distribution for airfoils with a high lift coefficient at the maximum lift to drag ratio. However, if the airfoil has a fairly low lift coefficient at its maximum lift to drag ratio due to its shape or a rough surface then significant improvement can be obtained in power coefficient by altering the Glauert chord and twist distribution according to the method proposed herein.

scholarly journals Study of board bending degree on hydrodynamic performances of a single-layer cambered otter-board

2019 ◽  
Vol 131 ◽  
pp. 01120
Author(s):  
Lei Wang ◽  
Lu Min Wang ◽  
Yong Li Liu ◽  
Wen Wen Yu ◽  
Guang Rui Qi ◽  
...  
Keyword(s):  
Center Of Pressure ◽  
Lift Coefficient ◽  
Pressure Coefficient ◽  
Angle Of Attack ◽  
Single Layer ◽  
Moment Coefficient ◽  
Pitch Moment ◽  
Engineering Models ◽  
Drag Ratio ◽  
Lift To Drag Ratio

The effect of board bending degree on hydrodynamic performances of a single-layer cambered otter-board was investigated using engineering models in a wind tunnel. Three different bending degree boards were evaluated at a wind speed of 28 m/s. Parameters measured included: drag coefficient Cx, lift coefficient Cy, pitch moment coefficient Cm, center of pressure coefficient Cp , over a range of angle of attack (0° to 70°). These coefficients were used in analyzing the differences in the performance among the three otter-board models. Results showed that the bending of the board(No. 2, No. 3) increased the water resistance of the otter-board, and improved the lift coefficient of the otter-board in the small angle of attack (0°<α≤20 °) ; the maximum lift coefficients Cy of otter-board model (No. 1) was higher (1.680, α = 25°). the maximum lift–drag ratios of models (No. 1, No. 2 and No. 3) are 6.822 (α = 7.5 °), 6.533 (α = 2.5 °) and 6.384 (α = 5.0°), which showed that the board bending reduces the lift-to-drag ratio of the otter-board.The stability of the No. 3 model was better than those two models (No. 1, No. 2) in most range of attack angle, but No. 1 otter-board model had a better stability in roll of otter-board. The findings of this study can offer useful reference data for the structural optimization of otter-boards for trawling.

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