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1.
Our previous study shows that the hovering and forward flight of a bumblebee do not have inherent stability (passive stability). But the bumblebees are observed to fly stably. Stabilization control must have been applied. In this study, we investigate the longitudinal stabilization control of the bumblebee. The method of computational fluid dynamics is used to compute the control derivatives and the techniques of eigenvalue and eigenvector analysis and modal decomposition are used for solving the equations of motion. Controllability analysis shows that at all flight speeds considered, although inherently unstable, the flight is controllable. By feedbacking the state variables, i.e. vertical and horizontal velocities, pitching rate and pitch angle (which can be measured by the sensory system of the insect), to produce changes in stroke angle and angle of attack of the wings, the flight can be stabilized, explaining why the bumblebees can fly stably even if they are passively unstable. 相似文献
2.
Flight agility, resistance to gusts, capability to hover coupled with a low noise generation might have been some of the reasons
why insects are among the oldest species observed in nature. Biologists and aerodynamicists focused on analyzing such flight
performances for diverse purposes: understanding the essence of flapping wings aerodynamics and applying this wing concept
to the development of micro-air vehicles (MAVs). In order to put into evidence the fundamentally non-linear unsteady mechanisms
responsible for the amount of lift generated by a flapping wing (Dickinson et al. in Science 284:1954–1960, 1999), experimental and numerical studies were carried out on typical insect model wings and kinematics. On the other hand, in
the recent context of MAVs development, it is of particular interest to study simplified non-biological flapping configurations
which could lead to lift and/or efficiency enhancement. In this paper, we propose a parametrical study of a NACA0012 profile
undergoing asymmetric hovering flapping motions at Reynolds 1000. On the contrary to normal hovering, which has been widely
studied as being the most common configuration observed in the world of insects, asymmetric hovering is characterized by an
inclined stroke plane. Besides the fact that the vertical force is hence a combination of both lift and drag (Wang in J Exp
Biol 207:1137–1150, 2004), the specificity of such motions resides in the vortex dynamics which present distinct behaviours, whether the upstroke
angle of attack leads to a partially attached or a strong separated flow, giving more or less importance to the wake capture
phenomenon. A direct consequence of the previous remarks relies on the enhancement of aerodynamic efficiency with asymmetry.
If several studies reported results based on the asymmetric flapping motion of dragonfly, only few works concentrated on parametrizing
asymmetric motions (e.g. Wang in Phys Rev Lett 85:2216–2219, 2000). The present study relies on TR-PIV measurements which allow determination of the vorticity fields and provide a basis to
evaluate the resulting unsteady forces through the momemtum equation approach. 相似文献
3.
4.
Insect wings usually are flexible and deform significantly under the combined inertial and aerodynamic load. To study the effect of wing flexibility on both lift and thrust production in forward flight, a two-dimensional numerical simulation is employed to compute the fluid–structure interaction of an elastic wing section translating in an inclined stroke plane while pitching around its leading ledge. The effects of the wing stiffness, mass ratio, stroke plane angle, and flight speed are considered. The results show that the passive pitching due to wing deformation can significantly increase thrust while either maintaining lift at the same level or increasing it simultaneously. Another important finding is that even though the wing structure and actuation kinematics are symmetric, chordwise deformation of the wing shows a larger magnitude during upstroke than during downstroke. The asymmetry is more pronounced when the wing has a low mass ratio so that the fluid-induced deformation is significant. Such an aerodynamic cause may serve as an additional mechanism for the asymmetric deformation pattern observed in real insects. 相似文献
5.
Aerodynamics and mechanisms of elementary morphing models for flapping wing in forward flight of bat
Large active wing deformation is a significant way to generate high aerodynamic forces required in bat's flapping flight. Besides the twisting, elementary morphing models of a bat wing are proposed, including wing-bending in the spanwise direction, wing-cambering in the chordwise direction, and wing area-changing. A plate of aspect ratio 3 is used to model a bat wing, and a three-dimensional unsteady panel method is used to predict the aerodynamic forces. It is found that the cambering model has great positive influence on the lift, followed by the area-changing model and then the bending model. Further study indicates that the vortex control is a main mechanism to produce high aerodynamic forces. The mechanisms of aerodynamic force enhancement are asymmetry of the cambered wing and amplification effects of wing area-changing and wing bending. Lift and thrust are generated mainly during downstroke, and they are almost negligible during upstroke by the integrated morphing model-wing. 相似文献
6.
Karim Mazaheri Abbas Ebrahimi 《Archive of Applied Mechanics (Ingenieur Archiv)》2010,80(11):1255-1269
Flapping wings are promising lift and thrust generators, especially for very low Reynolds numbers. To investigate aeroelastic
effects of flexible wings (specifically, wing’s twisting stiffness) on hovering and cruising aerodynamic performance, a flapping-wing
system and an experimental setup were designed and built. This system measures the unsteady aerodynamic and inertial forces,
power usage, and angular speed of the flapping wing motion for different flapping frequencies and for various wings with different
chordwise flexibility. Aerodynamic performance of the vehicle for both no wind (hovering) and cruise condition was investigated.
Results show how elastic deformations caused by interaction of inertial and aerodynamic forces with the flexible structure
may affect specific power consumption. This information was used here to find a more suitable structural design. The best
selected design in our tests performs up to 30% better than others (i.e., less energy consumption for the same lift or thrust
generation). This measured aerodynamic information could also be used as a benchmarking data for unsteady flow solvers. 相似文献
7.
Summary The aeroelastic response analysis of a coupled rotor/fuselage system is approached by iterative solution of the blade aeroelastic
response in the non-inertial reference frame fixed on the hub, and the periodic response of the fuselage in the inertial reference
frame. A model of the coupled system hinged with the flap and lag hinges, the pitching bearing which may not coincide with
the hinges, and the sweeping-blade configuration is established. The moderate-deflection beam theory and the two-dimensional
quasi-steady aerodynamic model are employed to model the aeroelastic blade, all the kinetic and inertial factors are taken
into account in a unified manner. A five-nodes, 15-DOFs pre-twisted nonuniform beam element is developed for the discretization
of the blade, three rigid-body-motion DOFs are introduced for the motion of the hinges and the bearing. The Hamilton's principle
is employed to evaluate the equation of motion of the blade. The derived nonlinear ordinary differential equations with time-dependent
periodic coefficients are solved by a modified quasi-linearization method, which is developed for the higher DOF periodic
system. The resulting periodic forces and moments exerted on the fuselage by all the blades are evaluated every time, when
the converged nonlinear periodic response of the blade is obtained under the consideration of the equilibrium of the blades.
The fuselage structure is simplified to be a beam structure, the governing equation is established in the inertial reference
frame and a two-nodes beam element is used to discretize the flexible fuselage. The periodic response of the fuselage is solved
by a simple shooting method. The iteration of the rotor/fuselage response is continued, until the aeroelastic responses of
the blade and the fuselage converge simultaneously. Both the hovering and the forward flight states can be considered. The
results of a computed numerical example by the developed program are presented to verify in practice the economy of the modeling
as well as the reliability and efficiency of the corresponding solving methods.
Received 4 May 1998; accepted 11 August 1998 相似文献
8.
Experimental investigation of the effect of chordwise flexibility on the aerodynamics of flapping wings in hovering flight 总被引:1,自引:0,他引:1
Ornithopters or mechanical birds produce aerodynamic lift and thrust through the flapping motion of their wings. Here, we use an experimental apparatus to investigate the effects of a wing's twisting stiffness on the generated thrust force and the power required at different flapping frequencies. A flapping wing system and an experimental set-up were designed to measure the unsteady aerodynamic and inertial forces, power usage and angular speed of the flapping wing motion. A data acquisition system was set-up to record important data with the appropriate sampling frequency. The aerodynamic performance of the vehicle under hovering (i.e., no wind) conditions was investigated. The lift and thrust that were produced were measured for different flapping frequencies and for various wings with different chordwise flexibilities. The results show the manner in which the elastic deformation and inertial flapping forces affect the dynamical behavior of the wing. It is shown that the generalization of the actuator disk theory is, at most, only valid for rigid wings, and for flexible wings, the power P varies by a power of about 1.0 of the thrust T. This aerodynamic information can also be used as benchmark data for unsteady flow solvers. 相似文献
9.
K. MazaheriA. Ebrahimi 《Journal of Fluids and Structures》2011,27(4):586-595
The aerodynamic performance of a flexible membrane flapping wing has been investigated here. For this purpose, a flapping-wing system and an experimental set-up were designed to measure the unsteady aerodynamic forces of the flapping wing motion. A one-component force balance was set up to record the temporal variations of aerodynamic forces. The flapping wing was studied in a large low-speed wind tunnel. The lift and thrust of this mechanism were measured for different flapping frequencies, angles of attack and for various wind tunnel velocities. Results indicate that the thrust increases with the flapping frequency. An increase in the wind tunnel speed and flow angle of attack leads to reduction in the thrust value and increases the lift component. The aerodynamic and performance parameters were nondimensionalized. Appropriate models were introduced which show its aerodynamic performance and may be used in the design process and also optimization of the flapping wing. 相似文献
10.
A method is reported here for calculating unsteady aerodynamics of hovering and flapping airfoil for two-dimensional flow
via the following improved methodologies: (a) a correct formulation of the problem using stream function (ψ) and vorticity
(ω) as dependent variables; (b) calculating loads and moment by a new method to solve the governing pressure Poisson equation
(PPE) in a truncated part of the computational domain on a nonstaggered grid; (c) accurate solution using high accuracy compact
difference scheme for the vorticity transport equation (VTE) and (d) accelerating the computations by using a high-order filter
after each time step of integration. These have been used to solve Navier–Stokes equation for flow past flapping and hovering
NACA 0014 and 0015 airfoils at typical Reynolds numbers relevant to the study of unsteady aerodynamics of micro air vehicle
(MAV) and insect/bird flight. 相似文献
11.
In this paper, results of numerical and experimental studies are presented for a flapping two-dimensional (2D)elliptic airfoil in a forward flight condition at a Reynolds number of 5000.The study is motivated by the experiment of Read et al. (2003), which shows that the thrust coefficient of a 2D NACA0012 airfoil deteriorated at high flapping frequency (or Strouhal number) when the induced effective angle of attack profile ceases to be a simple harmonic function in time. As to why non-simple-harmonic profile of effective angle of attack is detrimental to thrust generation is not fully understood. The paper is an attempt to address this issue by examining the flow mechanism, including near field flow structures and the associated transient aerodynamic forces and pressure field, responsible for the observed behavior. Our results show that thrust suppression can be attributed to an adverse suction effect due to high rotation rate of the airfoil and the presence of an attached leading edge vortex generated in the previous stroke. The results further show that the condition for best efficiency need not necessary coincides with the condition of best thrust performance; this observation has been made in past studies of flapping flight. 相似文献
12.
A flow control mechanism in wing flapping with stroke asymmetry during insect forward flight 总被引:5,自引:0,他引:5
A theoretical modeling approach as well as an unsteady analytical method is used to study aerodynamic characteristics of wing flapping with asymmetric stroke-cycles in connection with an oblique stroke plane during insect forward flight. It is revealed that the aerodynamic asymmetry between the downstroke and the upstroke due to stroke-asymmetrical flapping is a key to understand the flow physics of generation and modulation of the lift and the thrust. Predicted results for examples of given kinematics validate more specifically some viewpoints that the wing lift is more easily produced when the forward speed is higher and the thrust is harder, and the lift and the thrust are generated mainly during downstroke and upstroke, respectively. The effects of three controlling parameters, i.e. the angles of tilted stroke plane, the different downstroke duration ratios, and the different angles of attack in both down- and up-stroke, are further discussed. It is found that larger oblique angles of stroke planes generate larger thrust but smaller lift; larger downstroke duration ratios lead to larger thrust, while making little change in lift and input aerodynamic power; and again, a small increase of the angle of attack in downstroke or upstroke may cause remarkable changes in aerodynamic performance in the relevant stroke.The project supported by the National Natural Science Foundation of China (10072066, 90305009) and the Chinese Academy of Sciences (KJCX-SW-L04, KJCX2-SW-L2)The English text was polished by Ron Marshall. 相似文献
13.
Dynamic flight stability of hovering insects 总被引:5,自引:3,他引:2
The equations of motion of an insect with flapping wings are derived and then simplified to that of a flying body using the
“rigid body” assumption. On the basis of the simplified equations of motion, the longitudinal dynamic flight stability of
four insects (hoverfly, cranefly, dronefly and hawkmoth) in hovering flight is studied (the mass of the insects ranging from
11 to 1,648 mg and wingbeat frequency from 26 to 157 Hz). The method of computational fluid dynamics is used to compute the
aerodynamic derivatives and the techniques of eigenvalue and eigenvector analysis are used to solve the equations of motion.
The validity of the “rigid body” assumption is tested and how differences in size and wing kinematics influence the applicability
of the “rigid body” assumption is investigated. The primary findings are: (1) For insects considered in the present study
and those with relatively high wingbeat frequency (hoverfly, drone fly and bumblebee), the “rigid body” assumption is reasonable,
and for those with relatively low wingbeat frequency (cranefly and howkmoth), the applicability of the “rigid body” assumption
is questionable. (2) The same three natural modes of motion as those reported recently for a bumblebee are identified, i.e.,
one unstable oscillatory mode, one stable fast subsidence mode and one stable slow subsidence mode. (3) Approximate analytical
expressions of the eigenvalues, which give physical insight into the genesis of the natural modes of motion, are derived.
The expressions identify the speed derivative M
u (pitching moment produced by unit horizontal speed) as the primary source of the unstable oscillatory mode and the stable
fast subsidence mode and Z
w (vertical force produced by unit vertical speed) as the primary source of the stable slow subsidence mode.
The project supported by the National Natural Science Foundation of China (10232010 and 10472008). 相似文献
14.
The theory of a lifting surface is used to construct a model of three-dimensional unsteady flow past a pair of flapping wings in the regime of normal hovering flight. A numerical method is used to make an aero-dynamic calculation of the wings and find kinematics generating a lift sufficient for the flight of an insect. 相似文献
15.
Lift and power requirements of hovering insect flight 总被引:6,自引:0,他引:6
Lift and power requirements for hovering flight of eight species of insects are studied by solving the Navier-Stokes equation numerically. The solution provides velocity and pressure fields, from which unsteady aerodynamic forces and moments are obtained. The inertial torque of wing mass are computed analytically. The wing length of the insects ranges from 2 mm (fruit fly) to 52 mm (hawkmoth); Reynolds numbers Re (based on mean flapping speed and mean chord length) ranges from 75 to 3850. The primary findings are shown in the following: (1) Either small (R = 2mm, Re = 75), medium (R ≈ 10 mm, Re ≈ 500) or large (R ≈ 50 mm, Re ≈ 4 000) insects mainly employ the same high-lift mechanism, delayed stall, to produce lift in hovering flight. The midstroke angle of attack needed to produce a mean lift equal to the insect weight is approximately in the range of 25° to 45°, which is approximately in agreement with observation. (2) For the small insect (fruit fly) and for the medium and large insects with relatively small wingbeat frequency (cranefly, ladybird and hawkmoth), the specific power ranges from 18 to 39W·kg^-1 , the major part of the power is due to aerodynamic force, and the elastic storage of negative work does not change the specific power greatly. However for medium and large insects with relatively large wingbeat frequency (hover fly, dronefly, honey bee and bumble bee), the specific power ranges from 39 to 61 W·kg^-1 , the major part of the power is due to wing inertia, and the elastic storage of negative work can decrease the specific power by approximately 33%. (3) For the case of power being mainly contributed by aerodynamic force (fruit fly, cranefly, ladybird and hawkmoth), the specific power is proportional to the product of the wingbeat frequency, the stroke amplitude, the wing length and the drag-to-lift ratio. For the case of power being mainly contributed by wing inertia (hoverfly, dronefly, honey bee and bumble bee), the specific power (without elastic storage) is proportional to the product of the cubic of wingbeat frequency, the square of the stroke amplitude, the square of the wing length and the ratio of wing mass to insect mass. 相似文献
16.
昆虫拍翼方式的非定常流动物理再探讨 总被引:5,自引:0,他引:5
基于提出的理论模化方法来探讨昆虫拍翼方式的非定常流动物理. 以悬停飞行为
例,通过对拍翼运动的分析,不仅解释了昆虫利用高频拍翼的方式为何能够克服低雷诺数带
来的气动局限性(St \gg 1/Re),而且还指出高升力产生和调节的3个流动
控制因素:(1) 由于拍翼的变速运动即时引起了流体动力响应,这种附加惯性效应
可产生瞬时的高升力; (2) 保持前缘涡不脱离翼面有助于减少升力的下降;
(3) 增大后缘涡的强度并加速其脱离后缘能够有效地提高升力. 相似文献
17.
Qualitative and quantitative flow visualizations were performed on a flapping rigid plate to establish a quantitative method
for flow observation and evaluation of the force in the near field of a flapping wing. Flow visualization was performed qualitatively
with dye visualization and quantitatively with velocity measurements using stereo particle image velocimetry (PIV) on three
planes near the tip of the plate along its chord and oriented normally. By ensemble averaging the velocity fields of the same
phase angles, they represent a portion of the volume near the tip. Measurements were conducted with two flapping frequencies
to compare the flow structure. The second invariant of the deformation tensor visualized the leading edge and mid-chord vortices
around the plate appearing due to flow separation behind the plate while other vortical structures were visualized by streamlines.
These structures appear to be related to the dynamics of the leading edge vortex. Force analysis by integrating the phase-averaged
velocity field within a chosen control volume showed increases in the maxima of the magnitudes of the non-dimensional unsteady
force terms on the edge of the plate at the angles after the end of each stroke. The non-dimensional phase-averaged momentum
flux was similar for both flapping frequencies. 相似文献
18.
19.
Longitudinal flight dynamics of hovering micro-air-vehicles and insects is considered. The natural oscillatory flapping motion of the wing leads to time-periodic stability derivatives (aerodynamic loads due to perturbation in the body-motion variables). Hence these terms play the role of parametric excitation on the flight dynamics. The main objective of this work is to assess the effects of these aerodynamic-induced parametric excitation terms that are neglected by the averaging analysis. The method of multiple scales is used to determine a second-order uniform expansion for the response of the time-periodic system at hand. The proposed approach is applied to the hovering flight dynamics of five insects that cover a wide range of operating frequency ratios to assess the applicability of the averaging analysis. 相似文献