scholarly journals The control of flight force by a flapping wing: lift and drag production

2001 ◽  
Vol 204 (15) ◽  
pp. 2607-2626 ◽  
Author(s):  
Sanjay P. Sane ◽  
Michael H. Dickinson
Keyword(s):  
High Performance ◽  
Time Course ◽  
Aerodynamic Force ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Force Sensor ◽  
Aerodynamic Forces ◽  
Wing Kinematics ◽  
The Mean ◽  
Stroke Amplitude

SUMMARYWe used a dynamically scaled mechanical model of the fruit fly Drosophila melanogaster to study how changes in wing kinematics influence the production of unsteady aerodynamic forces in insect flight. We examined 191 separate sets of kinematic patterns that differed with respect to stroke amplitude, angle of attack, flip timing, flip duration and the shape and magnitude of stroke deviation. Instantaneous aerodynamic forces were measured using a two-dimensional force sensor mounted at the base of the wing. The influence of unsteady rotational effects was assessed by comparing the time course of measured forces with that of corresponding translational quasi-steady estimates. For each pattern, we also calculated mean stroke-averaged values of the force coefficients and an estimate of profile power. The results of this analysis may be divided into four main points.(i) For a short, symmetrical wing flip, mean lift was optimized by a stroke amplitude of 180° and an angle of attack of 50°. At all stroke amplitudes, mean drag increased monotonically with increasing angle of attack. Translational quasi-steady predictions better matched the measured values at high stroke amplitude than at low stroke amplitude. This discrepancy was due to the increasing importance of rotational mechanisms in kinematic patterns with low stroke amplitude.(ii) For a 180° stroke amplitude and a 45° angle of attack, lift was maximized by short-duration flips occurring just slightly in advance of stroke reversal. Symmetrical rotations produced similarly high performance. Wing rotation that occurred after stroke reversal, however, produced very low mean lift.(iii) The production of aerodynamic forces was sensitive to changes in the magnitude of the wing’s deviation from the mean stroke plane (stroke deviation) as well as to the actual shape of the wing tip trajectory. However, in all examples, stroke deviation lowered aerodynamic performance relative to the no deviation case. This attenuation was due, in part, to a trade-off between lift and a radially directed component of total aerodynamic force. Thus, while we found no evidence that stroke deviation can augment lift, it nevertheless may be used to modulate forces on the two wings. Thus, insects might use such changes in wing kinematics during steering maneuvers to generate appropriate force moments.(iv) While quasi-steady estimates failed to capture the time course of measured lift for nearly all kinematic patterns, they did predict with reasonable accuracy stroke-averaged values for the mean lift coefficient. However, quasi-steady estimates grossly underestimated the magnitude of the mean drag coefficient under all conditions. This discrepancy was due to the contribution of rotational effects that steady-state estimates do not capture. This result suggests that many prior estimates of mechanical power based on wing kinematics may have been grossly underestimated.

scholarly journals Plunging Airfoil: Reynolds Number and Angle of Attack Effects

Aerospace ◽  
2021 ◽  
Vol 8 (8) ◽  
pp. 216
Author(s):  
Emanuel A. R. Camacho ◽  
Fernando M. S. P. Neves ◽  
André R. R. Silva ◽  
Jorge M. M. Barata
Keyword(s):  
Reynolds Number ◽  
High Performance ◽  
Angle Of Attack ◽  
Systems Design ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Low Reynolds Numbers ◽  
Operational Conditions ◽  
Naca0012 Airfoil ◽  
The Mean

Natural flight has consistently been the wellspring of many creative minds, yet recreating the propulsive systems of natural flyers is quite hard and challenging. Regarding propulsive systems design, biomimetics offers a wide variety of solutions that can be applied at low Reynolds numbers, achieving high performance and maneuverability systems. The main goal of the current work is to computationally investigate the thrust-power intricacies while operating at different Reynolds numbers, reduced frequencies, nondimensional amplitudes, and mean angles of attack of the oscillatory motion of a NACA0012 airfoil. Simulations are performed utilizing a RANS (Reynolds Averaged Navier-Stokes) approach for a Reynolds number between 8.5×103 and 3.4×104, reduced frequencies within 1 and 5, and Strouhal numbers from 0.1 to 0.4. The influence of the mean angle-of-attack is also studied in the range of 0∘ to 10∘. The outcomes show ideal operational conditions for the diverse Reynolds numbers, and results regarding thrust-power correlations and the influence of the mean angle-of-attack on the aerodynamic coefficients and the propulsive efficiency are widely explored.

scholarly journals Experimental Investigation of Lift Enhancement and Drag Reduction of Discrete Co-Flow Jet Rotor Airfoil

2021 ◽  
Vol 11 (20) ◽  
pp. 9561
Author(s):  
Shunlei Zhang ◽  
Xudong Yang ◽  
Bifeng Song ◽  
Zhuoyuan Li ◽  
Bo Wang
Keyword(s):  
Drag Reduction ◽  
High Performance ◽  
Performance Enhancement ◽  
Fundamental Problem ◽  
Unit Length ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Relative Unit ◽  
Lift Enhancement ◽  
Stall Angle

Rotor airfoil design involves multi-point and multi-objective complex constraints. How to significantly improve the maximum lift coefficient and lift-to-drag ratio of rotor airfoil is a fundamental problem, which should be solved urgently in the development of high-performance helicopter rotor blades. To address this, discrete co-flow jet (DCFJ) technology is one methods with the most potential that can be harnessed to improve the performance of the rotor airfoil. In this study, wind tunnel experiments are conducted to study the effect of DCFJ technology on lift enhancement and drag reduction of OA312 airfoil. Furthermore, the performance improvement effects of the open co-flow jet (CFJ) and DCFJ technologies are studied. In addition, the influence of fundamental parameters, such as the obstruction factor and relative unit length, are analyzed. Results demonstrate that DCFJ technology is better than CFJ technology on the performance enhancement of the OA312 airfoil. Moreover, the DCFJ rotor airfoil can significantly reduce the drag coefficient and increase the maximum lift coefficient and the stall angle of attack. The maximum lift coefficient can be increased by nearly 67.3%, and the stall angle of attack can be delayed by about 12°. The DCFJ rotor airfoil can achieve the optimal performance when the obstruction factor is 1/2 and the relative unit length is 0.025.

Unsteady aerodynamic force generation by a model fruit fly wing in flapping motion

2002 ◽  
Vol 205 (1) ◽  
pp. 55-70 ◽  
Author(s):  
Mao Sun ◽  
Jian Tang
Keyword(s):  
Aerodynamic Force ◽  
Lift Coefficient ◽  
Unsteady Aerodynamics ◽  
Fruit Fly ◽  
Force Generation ◽  
Generation Process ◽  
Flapping Motion ◽  
Unsteady Aerodynamic ◽  
The Mean ◽  
Unsteady Aerodynamic Force

SUMMARY A computational fluid-dynamic analysis was conducted to study the unsteady aerodynamics of a model fruit fly wing. The wing performs an idealized flapping motion that emulates the wing motion of a fruit fly in normal hovering flight. The Navier–Stokes equations are solved numerically. The solution provides the flow and pressure fields, from which the aerodynamic forces and vorticity wake structure are obtained. Insights into the unsteady aerodynamic force generation process are gained from the force and flow-structure information. Considerable lift can be produced when the majority of the wing rotation is conducted near the end of a stroke or wing rotation precedes stroke reversal (rotation advanced), and the mean lift coefficient can be more than twice the quasi-steady value. Three mechanisms are responsible for the large lift: the rapid acceleration of the wing at the beginning of a stroke, the absence of stall during the stroke and the fast pitching-up rotation of the wing near the end of the stroke. When half the wing rotation is conducted near the end of a stroke and half at the beginning of the next stroke (symmetrical rotation), the lift at the beginning and near the end of a stroke becomes smaller because the effects of the first and third mechanisms above are reduced. The mean lift coefficient is smaller than that of the rotation-advanced case, but is still 80 % larger than the quasi-steady value. When the majority of the rotation is delayed until the beginning of the next stroke (rotation delayed), the lift at the beginning and near the end of a stroke becomes very small or even negative because the effect of the first mechanism above is cancelled and the third mechanism does not apply in this case. The mean lift coefficient is much smaller than in the other two cases.

scholarly journals Scaling of the performance of insect-inspired passive-pitching flapping wings

2019 ◽  
Vol 16 (161) ◽  
pp. 20190609 ◽  
Author(s):  
Kit Sum Wu ◽  
Jerome Nowak ◽  
Kenneth S. Breuer
Keyword(s):  
Scaling Laws ◽  
Aerodynamic Force ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Flapping Wing ◽  
Dimensionless Parameters ◽  
Linear Elastic ◽  
Simple Implementation ◽  
Pitch Regulation ◽  
Cauchy Number

Flapping flight using passive pitch regulation is a commonly used mode of thrust and lift generation in insects and has been widely emulated in flying vehicles because it allows for simple implementation of the complex kinematics associated with flapping wing systems. Although robotic flight employing passive pitching to regulate angle of attack has been previously demonstrated, there does not exist a comprehensive understanding of the effectiveness of this mode of aerodynamic force generation, nor a method to accurately predict its performance over a range of relevant scales. Here, we present such scaling laws, incorporating aerodynamic, inertial and structural elements of the flapping-wing system, validating the theoretical considerations using a mechanical model which is tested for a linear elastic hinge and near-sinusoidal stroke kinematics over a range of scales, hinge stiffnesses and flapping frequencies. We find that suitably defined dimensionless parameters, including the Reynolds number, Re , the Cauchy number, Ch , and a newly defined ‘inertial-elastic’ number, IE, can reliably predict the kinematic and aerodynamic performance of the system. Our results also reveal a consistent dependency of pitching kinematics on these dimensionless parameters, providing a connection between lift coefficient and kinematic features such as angle of attack and wing rotation.

Aerodynamic Forces on a Simplified Car Body: Towards Innovative Designs for Car Drag Reduction

2010 ◽  
Author(s):  
Mahmoud Khaled ◽  
Fabien Harambat ◽  
Anthony Yammine ◽  
Hassan Peerhossaini
Keyword(s):  
Drag Reduction ◽  
Drag Coefficient ◽  
Aerodynamic Drag ◽  
Cooling System ◽  
Aerodynamic Force ◽  
Lift Coefficient ◽  
Force Measurements ◽  
Vehicle Model ◽  
Aerodynamic Forces ◽  
Aerodynamic Drag Reduction

The present paper exposes the study of the cooling system circulation effect on the external aerodynamic forces. We report here aerodynamic force measurements carried out on a simplified vehicle model in wind tunnel. Tests are performed for different airflow configurations in order to detect the parameters that can affect the aerodynamic torsor and to confirm others previously suspected, especially the air inlets localization, the air outlet distributions and the underhood geometry. The simplified model has flat and flexible air inlets and several types of air outlet, and includes in its body a real cooling system and a simplified engine block that can move in the longitudinal and lateral directions. The results of this research are generic and can be applied to any new car design. Results show configurations in which, with respect to the most commonly adopted underhood geometries, the overall drag coefficient can be decreased by 2%, the aerodynamic cooling drag coefficient by more than 50% and the lift coefficient by 5%. Finally, new designs of aerodynamic drag reduction, based on the combined effects of the different investigated parameters, are proposed.

scholarly journals An Experimental Analysis on the Effects of Stagger on the Aerodynamic Forces of Tandem Wings

AVIA ◽  
2021 ◽  
Vol 2 (2) ◽  
Author(s):  
Y Parlindungan ◽  
S Tobing
Keyword(s):  
Experimental Analysis ◽  
Numerical Study ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Aerodynamic Performance ◽  
Open Loop ◽  
Aerodynamic Forces ◽  
Subsonic Wind Tunnel ◽  
Lift And Drag ◽  
Naca 0012

This study is inspired by the flapping motion of natural flyers: insects. Many insects have two pairs of wings referred as tandem wings. Literature review indicates that the effects of tandem wing are influenced by parameters such as stagger (the stream-wise distance between the aerodynamic center of the front and the rear airfoil), angle-of-attack and flow velocity. As a first stage, this study focuses on the effects of stagger (St) on the aerodynamic performance of tandem wings. A recent numerical study of stagger on tandem airfoils in turbulent flow (Re = 6000000) concluded that a larger stagger resulted in a decrease in lift force, and an increase in drag force. However, for laminar flow (Re = 2000), increasing the stagger was not found to be detrimental for aerodynamic performance. Another work also revealed that the maximum lift coefficient for a tandem configuration decreased with increasing stagger. The focus of this study is to perform an experimental analysis of tandem two-dimensional (2D) NACA 0012 airfoils. The two airfoils are set at the same angle-of-attack of 0° to 15° with 5° interval and three variations of stagger: 1c, 1.5c and 2c. The experiments are conducted using an open-loop-subsonic wind tunnel at a Reynolds number of 170000. The effects of St on the aerodynamic forces (lift and drag) are analyzed

scholarly journals On the aerodynamic forces on heaving and pitching airfoils at low Reynolds number

2017 ◽  
Vol 828 ◽  
pp. 395-423 ◽  
Author(s):  
M. Moriche ◽  
O. Flores ◽  
M. García-Villalba
Keyword(s):  
Aerodynamic Force ◽  
The Body ◽  
Body Motion ◽  
Fluid Inertia ◽  
Aerodynamic Forces ◽  
Noticeable Improvement ◽  
Large Amplitude Motions ◽  
Flow Circulation ◽  
The Mean ◽  
Force Decomposition

The influence that the kinematics of pitching and heaving 2D airfoils has on the aerodynamic forces is investigated using direct numerical simulations and a force decomposition algorithm. Large-amplitude motions are considered (of the order of one chord), with moderate Reynolds numbers and reduced frequencies of order $O(1)$, varying the mean pitch angle and the phase shift between the pitching and heaving motions. Our results show that the surface vorticity contribution (viscous effect) to the aerodynamic force is negligible compared with the contributions from the body motion (fluid inertia) and the vorticity within the flow (circulation). For the range of parameters considered here, the latter tends to be instantaneously oriented in the direction normal to the chord of the airfoil. Based on the results discussed in this paper, a reduced-order model for the instantaneous aerodynamic force is proposed, taking advantage of the force decomposition and the chord-normal orientation of the contribution from vorticity within the flow to the total aerodynamic force. The predictions of the proposed model are compared with those of a similar model from the literature, showing a noticeable improvement in the prediction of the mean thrust, and a smaller improvement in the prediction of the mean lift and the instantaneous force coefficients.

Advantages of an Ornithopter against an Airplane with a Propeller

2012 ◽  
Vol 84 ◽  
pp. 66-71
Author(s):  
Shigeru Sunada
Keyword(s):  
High Performance ◽  
Aerodynamic Force ◽  
Micro Air Vehicle ◽  
Wind Gust ◽  
Aerodynamic Forces ◽  
Promising Candidate ◽  
Flapping Motion ◽  
Wind Gusts ◽  
Air Vehicle ◽  
Before And After

The goal of our research is to develop a micro air vehicle (MAV) that is strongly stable in a wind gust. After observation of flights of an insect and a bird, we conjectured that an ornithopter would be a promising candidate as a high-performance MAV. In this paper we demonstrate the clear advantage of an ornithopter over an airplane with propellers. The variations in the aerodynamic forces acting on the two aircrafts, which generate the same thrust under the condition of no wind gust, were compared when they encountered gusts of wind. The consumed power, or alternately the period of one cycle of flapping motion and that of one rotation of propeller(s), remained constant before and after they encountered a wind gust. The following results were obtained: The variations of the aerodynamic force of an ornithopter by vertical and frontal wind gusts were slightly smaller than those of an airplane with one or two propellers. The variation in the aerodynamic force of the former by a side wind gust was smaller than that of the latter when the tip speed of the propeller and the flapping amplitude of the ornithopter were small.

Vortex force of an impulsively started plate at high angle of attack

2017 ◽  
Vol 27 (11) ◽  
pp. 2402-2414
Author(s):  
Xiang Fu ◽  
Gaohua Li ◽  
Fuxin Wang
Keyword(s):  
Aerodynamic Force ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Aerodynamic Forces ◽  
Total Drag ◽  
Content Type ◽  
Vortical Structures ◽  
Edge Vortex ◽  
The Individual ◽  
Practical Implications

Purpose A quantitative study that can identify the primary aerodynamic forces and relate them to individual vortical structures is lacking. The paper aims to clarify the quantitative relationships between the aerodynamic forces and vortical structures. Design/methodology/approach The various contributions to the aerodynamic forces on the two-dimensional impulsively started plate are investigated from the perspective of the vorticity moment theorem. The angles of attacks are set to 45°, 58.5° and 72°, while the Reynolds number is 10,000 based on the chord length. Compared with the traditional pressure force analysis, this theorem not only tells us the total aerodynamic force during the motion, but also enables us to quantify the forces contributed from the fluid elements with non-zero vorticity. Findings It is found that the time-dependent force behaviors are dominated by the formations and evolutions of these vortical structures. The analysis of the time-averaged forces demonstrates that the lift contributed from the leading edge vortex (LEV) is nearly four times larger than the total lift and the drag contributed from the starting vortex (SV) is almost equal to the total drag when the angle of attack (AoA) increases to 72°, which means the LEV is “lift structure” whereas the SV is “drag structure”. Practical implications The present method provides a better perspective for flow control and drag reduction by relating the forces directly to the individual vorticity structures. Originality/value In this paper, the Vorticity Moment Theory is first used to study the quantitative relationships between the aerodynamic forces and the vortices.

scholarly journals Parametric study of a corrugated airfoil in a forward flight at ultra-low Reynolds number

2021 ◽  
Vol 3 (1) ◽  
Author(s):  
Mahmoud E. Abd El-Latief ◽  
Khairy Elsayed ◽  
Mohamed M. Abdelrahman
Keyword(s):  
Reynolds Number ◽  
Phase Difference ◽  
Lift Force ◽  
Thrust Force ◽  
Angle Of Attack ◽  
Initial Angle ◽  
Aerodynamic Forces ◽  
Forward Flight ◽  
Propulsive Efficiency ◽  
Stroke Amplitude

AbstractIn the current study, the mid cross section of the dragonfly forewing was simulated at ultra-low Reynolds number. The study aims to understand better the contribution of corrugations found along the wing on the aerodynamic performance during a forward flight. Different flapping parameters were employed. FLUENT solver was used to solve unsteady, two-dimensional, laminar, incompressible Navier–Stokes equations. The results revealed that any stroke amplitude less than 1cm generated no thrust force. The stroke amplitude had to be increased to form the reversed Kármán vortices responsible for generating thrust force. The highest propulsive efficiency was found in the Strouhal number range 0.2 < St < 0.4 with a peak efficiency of 57% at St = 0.39. Changing the phase difference between pitching and plunging motions from advanced to synchronized caused lift force to drop 91% and thrust force to increase by 15%. On the other hand, changing the phase difference from synchronized to delayed caused lift and thrust forces to increase by 89% and 36%, respectively, and propulsive efficiency to deteriorate significantly. In all performed simulations, the airfoil was assumed to start motion from rest with no initial angle of attack. The increase in initial angle of attack generates a very high lift force with a fair loss for both thrust force and propulsive efficiency. The decomposition of flapping motion into its elementary motions revealed that the aerodynamic forces generated are a non-linear superposition from both pure pitching and pure plunging aerodynamic forces. This can be attributed to the non-linear interaction between unsteady vortices generated from these decomposed motions.

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