飞行器纵向俯仰气动特性计算研究

应用有限体积方法求解三维可压缩雷诺平均N-S方程,计算了巡航导弹外形飞行器作小振幅俯仰运动时的动态绕流流场和空气动力特性,开展了导弹绕不同转轴、以不同频率和在不同迎角范围内进行俯仰运动的非定常气动力迟滞特性研究。计算结果表明,当导弹作快速俯仰运动时,在上仰和下俯过程中的同一迎角瞬间,绕导弹流场流动明显不同,表现出明显的非定常迟滞特性。导弹的非定常气动力迟滞特性随俯仰运动频率的增大明显增强,且气动力迟滞曲线随着俯仰轴位置的变化而变化。在同一减缩频率下,导弹在不同迎角范围内作周期俯仰运动时,相同的运动相位角所对应的升力系数对迎角的导数是一致的,而不同减缩频率下升力系数对迎角的导数随运动相位角变化曲线明显不同。     

Near wake vortex dynamics of a hovering hawkmoth

Numerical investigation of vortex dynamics in near wake of a hovering hawkmoth and hovering aerodynamics is conducted to support the development of a biology-inspired dynamic flight simulator for flapping wingbased micro air vehicles. Realistic wing-body morphologies and kinematics are adopted in the numerical simulations. The computed results show 3D mechanisms of vortical flow structures in hawkmoth-like hovering. A horseshoe-shaped primary vortex is observed to wrap around each wing during the early down- and upstroke; the horseshoe-shaped vortex subsequently grows into a doughnut-shaped vortex ring with an intense jet-flow present in its core, forming a downwash. The doughnut-shaped vortex rings of the wing pair eventu- ally break up into two circular vortex rings as they propagate downstream in the wake. The aerodynamic yawing and rolling torques are canceled out due to the symmetric wing kinematics even though the aerodynamic pitching torque shows significant variation with time. On the other hand, the time- varying the aerodynamics pitching torque could make the body a longitudinal oscillation over one flapping cycle.     

UNCONDITIONAL STABLE SOLUTIONS OF THE EULER EQUATIONS FOR TWO－AND THREE－D WINGS IN ARBITRARY MOTION

ＵＮＣＯＮＤＩＴＩＯＮＡＬＳＴＡＢＬＥＳＯＬＵＴＩＯＮＳＯＦＴＨＥＥＵＬＥＲＥＱＵＡＴＩＯＮＳＦＯＲＴＷＯ－ＡＮＤＴＨＲＥＥ－ＤＷＩＮＧＳＩＮＡＲＢＩＴＲＡＲＹＭＯＴＩＯＮＧａｏＺｈｅｎｇｈｏｎｇ（高正红）（ＲｅｃｅｉｖｅｄＪａｎ．１２,１９９５,Ｃ...     

等速上仰翼型动态失速现象研究

翼型大迎角绕流的静态失速将造成升力突降和气动性能急剧恶化，但利用非定常运动所产生 的动态失速效应，可以大大地延缓气流分离和失速现象的发生. 采用Rogers发 展的双时间步Roe格式，求解拟压缩性修正不可压N-S方程. 数值模拟了低雷诺数 ($Re=4.8 \times 10^{4}$)条件下NACA0015翼型作等速上仰($\alpha =0^{\circ} \sim 60^{\circ}$)的动态失速过程，同Walker的试验结果比 较，验证了计算结果的正确性. 研究了该过程中主涡、二次涡和三次涡的发展，升 力系数随攻角变化，以及不同上仰速度对动态失速效应所造成的影响.     

基于流形切空间插值的折叠翼参数化气动弹性建模

变体飞行器的气动弹性力学建模是当前先进飞行器设计的研究热点和难点.然而传统的气动弹性动力学建模方法对于具有结构参变特性的变体飞行器气动弹性力学研究存在建模效率低、计算复杂等问题.本研究提出了一种基于流形切空间插值的可折叠式变体机翼参数化气动弹性建模方法.首先,该方法建立若干个典型折叠角下的折叠翼结构有限元模型,通过流形...     

Numerical simulation of flapping‐wing insect hovering flight at unsteady flow

A computational fluid dynamics (CFD) analysis was conducted to study the unsteady aerodynamics of a virtual flying bumblebee during hovering flight. The integrated geometry of bumblebee was established to define the shape of a three‐dimensional virtual bumblebee model with beating its wings, accurately mimicking the three‐dimensional movements of wings during hovering flight. The kinematics data of wings documented from the measurement to the bumblebee in normal hovering flight aided by the high‐speed video. 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. The CFD analysis has established an overall understanding of the viscous and unsteady flow around the virtual flying bumblebee and of the time course of instantaneous force production, which reveals that hovering flight is dominated by the unsteady aerodynamics of both the instantaneous dynamics and also the past history of the wing. A coherent leading‐edge vortex with axial flow and the attached wingtip vortex and trailing edge vortex were detected. The leading edge vortex, wing tip vortex and trailing edge vortex, which caused by the pressure difference between the upper and the lower surface of wings. The axial flow, which include the spanwise flow and chordwise flow, is derived from the spanwise pressure gradient and chordwise pressure gradient, will stabilize the vortex and gives it a characteristic spiral conical shape. Copyright © 2006 John Wiley & Sons, Ltd.     

An analytic approach to theoretical modeling of highly unsteady viscous flow excited by wing flapping in small insects

Numerous studies on the aerodynamics of insect wing flapping were carried out on different approaches of flight investigations, model experiments, and numerical simulations, but the theoretical modeling remains to be explored. In the present paper, an analytic approach is presented to model the flow interactions of wing flapping in air for small insects with the surrounding flow fields being highly unsteady and highly viscous. The model of wing flapping is a 2-D flat plate, which makes plunging and pitching oscillations as well as quick rotations reversing its positions of leading and trailing edges, respectively, during stroke reversals. It contains three simplified aerodynamic assumptions: (i) unsteady potential flow; (ii) discrete vortices shed from both leading and trailing edges of the wing; (iii) Kutta conditions applied at both edges. Then the problem is reduced to the solution of the unsteady Laplace equation, by using distributed singularities, i.e., sources/sinks, and vortices in the field. To validate the present physical model and analytic method proposed via benchmark examples, two elemental motions in wing flapping and a case of whole flapping cycles are analyzed, and the predicted results agree well with available experimental and numerical data. This verifies that the present analytical approach may give qualitatively correct and quantitatively reasonable results. Furthermore, the total fluid-dynamic force in the present method can be decomposed into three parts: one due to the added inertial (or mass) effect, the other and the third due to the induction of vortices shed from the leading-and the trailing-edge and their images respectively, and this helps to reveal the flow control mechanisms in insect wing flapping. The project supported by the National Natural Science Foundation of China (10072066) and the Chinese Academy of Sciences (KJCX-SW-LO4, KJCX2-SW-L2)     

NUMERICAL SIMULATION STUDY ON DYNAMIC RESPONSE UNDER RUDDER CONTROL

针对超声速机动飞行器舵面操纵动态响应问题,开展了相应的算法研究,建立了适用于模拟舵面与弹体相对运动及弹体气动力动态响应的非定常计算方法和局部动态网格变形技术. 以方形弹超声速绕流为例,验证了所提出的定常和非定常计算方法. 对方形弹舵面操纵的3种基本过程(脉冲、阶跃和谐波) 进行了数值模拟,获得了舵面操纵下导弹的俯仰运动对操纵的响应过程. 研究结果表明,快速的舵面操纵过程,甚至会导致导弹的俯仰运动失稳.     

An investigation into the effects of unsteady parameters on the aerodynamics of a low Reynolds number pitching airfoil

The growing applications of low Reynolds number (LRN) operating vehicles impose the need for accurate LRN flow solutions. These applications usually involve complex unsteady phenomena, which depend on the kinematics of the vehicle such as pitching, plunging, and flapping of a wing. The objective of the present study is to address the issues related to LRN aerodynamics of a harmonically pitching NACA0012 airfoil. To this end, the influence of unsteady parameters, namely, amplitude of oscillation, d, reduced frequency, k, and Reynolds number, Re, on the aerodynamic performance of the model is investigated. Computational fluid dynamics (CFD) is utilized to solve Navier–Stokes (N–S) equations discretized based on the Finite Volume Method (FVM). The resulting instantaneous lift coefficients are compared with analytical data from Theodorsen’s method. The simulation results reveal that d, k, and Re are of great importance in the aerodynamic performance of the system, as they affect the maximum lift coefficients, hysteresis loops, strength, and number of the generated vortices within the harmonic motion, and the extent of the so-called figure-of-eight phenomenon region. Thus, achieving the optimum lift coefficients demands a careful selection of these parameters.     

基于传递函数法的带多个外挂机翼颤振分析

基于带外挂机翼结构和气动特点，使用带有半解析半数值特性的传递函数方法进行处理．首先，通过机翼的运动微分方程、二元机翼非定常气动力Therdorson 模型、结合外挂挂载处的内力平衡与位移状态条件，得到了三维的带多个外挂大展弦比机翼的颤振微分方程．进而，使用传递函数方法，先将颤振计算方程整理成为状态空间方程形式，结合求解复特征值的方法，完成了带多个外挂大展弦比机翼的动气动弹性稳定性分析．对比已有文献的计算结果以及通过有限元方法进行的仿真结果，证实了文章所提计算方法的准确性和高效性，结合传递函数方法的优势，进一步将文章方法拓展到机翼的固有频率和发散速度求解．文章结尾，分析了外挂数量、外挂质量、转动惯量及位置分布等变量对带多个外挂大展弦比机翼的动气动弹性稳定性的影响．     

Computational study of a pitching bio-inspired corrugated airfoil

The phenomenon of insect flight has been of scientific interest for many years and is more recently inspiring modern engineering devices such as Micro Aerial Vehicles (MAVs). Insect flight is characterized by unsteady fluid dynamics at low Reynolds numbers. The importance of viscous effects to the successful flapping flight of insects has been identified and with the current state of computing and Computational Fluid Dynamics (CFD) these effects can now be studied in detail. The present work attempts to simplify this complex phenomenon by considering symmetric oscillating rotational motion of a wing (pitching). What is of interest in this study is how the shape of a corrugated idealized insect wing affects the performance and flow characteristics around the pitching wing. Two dimensional CFD on an oscillating wing has been performed and reported. Measurements were taken to ensure the accuracy of the computational solution and the results validated against experimental PIV results. A range of frequencies and rotational amplitudes have been investigated. Lift and drag coefficients have been analyzed for all cases to quantify the effects of unsteady flow features on the performance of the oscillating wing. It was found that the wing shape used in this study resulted in the viscous features formed on the top of the wing exhibiting high sensitivity to the oscillating conditions and these influenced the performance of the wing. The flow features formed on the bottom of the wing remained similar throughout the cases tested. In the pitching regime this wing profile did not perform as well as published results for smooth airfoils in terms of thrust and propulsion efficiency. However this may be due to reduced frequency effects becoming important at our high pitching amplitude which need to be investigated further. There may be other oscillatory regimes that more accurately represent flapping flight in which the corrugated foil outperforms a smooth counterpart but these are yet to be investigated. Further research in this area may help answer the question as to how evolutionarily significant other benefits of a corrugated wing, such as being light and strong, are compared to its aerodynamic properties, the present results seem to favor the former.     

智能物面对非定常分离流的最优自适应控制

以低雷诺数二维大攻角翼型绕流为研究对象, 将非定常动边界计算流体力学方法与 最优控制方法有机结合, 研究二维不可压非定常流智能物面最优自适应流 动控制的理论与算法, 并将其用于固定攻角和俯仰振荡翼型绕流. 结果表明: 在给定合适的最优控制目标函数下, 智能物面可最优地实时改变形状, 得到能显著提高翼型性能的最优翼型. 最优翼型在非设计工况下的气动性能也比对照翼型有 所提高.     

Experimental study of the flow field induced by a resonating piezoelectric flapping wing

Flexible plate structures with integrated piezoelectric patches offer interesting possibilities when considered as actuation mechanisms for energy harvesting devices, cooling devices and propulsion devices of micro-aerial vehicles. Most of the studies reported in literature are based on the assumption of a 2D aerodynamic flow. However, the flow behind a finite span wing is significantly more complex than that of an infinite span wing. In order to corroborate this statement, the present experimental study contains high-speed particle image velocimetry measurements performed on a piezoelectric finite span wing oscillating in air, at 84.8 Hz. The paper focuses on the situation of low Keulegan–Carpenter numbers (KC < 3). The dimensionless KC number describes the relative importance of the drag forces over inertia forces for objects that oscillate in a fluid flow at rest. The evolution of the unsteady vortex structures near the plate is characterized for different conditions. This allows a better understanding of the unsteady aerodynamics of flapping flight. The accomplished experimental data analysis has shown that the flow phenomena are strongly dependent on the KC values.     

A parametric investigation of the propulsion of 2D chordwise-flexible flapping wings at low Reynolds number using numerical simulations

This paper presents a numerical investigation of the effects of chordwise flexibility on flapping wings at low Reynolds number. The numerical simulations are performed with a partitioned fluid–structure interaction algorithm using artificial compressibility stabilization. The choice of the structural dimensionless parameters is based on scaling arguments and is compared against parameters used by other authors. The different regimes, namely inertia-driven and pressure-driven wing deformations, are presented along with their effects on the topology of the flow and on the performance of a heaving and pitching flapping wing in propulsion regime. It is found that pressure-driven deformations can significantly increase the thrust efficiency if a suitable amount of flexibility is used. Significant thrust increases are also observed in zero pitching amplitude cases. The effects of the second and third deformation modes on the performances of pressure-driven deformation cases are discussed. On the other hand, inertia-driven deformations generally deteriorate aerodynamic performances of flapping wings unless the behavior of the wing deformation is modified by the presence of sustainable superharmonics in a way that produces slight improvements. It is also shown that wing flexibility can act as an efficient passive pitching mechanism that allows fair thrust and better efficiency to be achieved when compared to a rigid pitching–heaving wing.     

旋转流场下模型大幅俯仰运动实验研究

在中航气动院FL-8低速风洞中,采用单自由度振荡机构进行了旋转流场下大幅俯仰运动的气动特性实验研究。模型在绕风速轴连续旋转的同时,进行给定频率和振幅绕体轴的俯仰振荡运动。测量了模型的动态气动特性,着重分析了不同运动参数对模型气动特性的影响。实验结果表明,旋转速度的存在使大振幅俯仰振荡实验中的滚转力矩和偏航力矩产生了明显的迟滞特性,但对俯仰力矩和法向力的迟滞特性影响不大。     

Unsteady aerodynamics modeling for flight dynamics application

In view of engineering application, it is practicable to decompose the aerodynamics into three components: the static aerodynamics, the aerodynamic increment due to steady rotations, and the aerodynamic increment due to unsteady separated and vortical flow. The first and the second components can be presented in conventional forms while the third is described using a one-order differential equation and a radial-basis-function (RBF) network. For an aircraft configuration, the mathematical models of 6component aerodynamic coefficients are set up from the wind tunnel test data of pitch, yaw, roll, and coupled yawroll large-amplitude oscillations. The flight dynamics of an aircraft is studied by the bifurcation analysis technique in the case of quasi-steady aerodynamics and unsteady aerodynamics, respectively. The results show that: (1) unsteady aerodynamics has no effect upon the existence of trim points, but affects their stability; (2) unsteady aerodynamics has great effects upon the existence, stability, and amplitudes of periodic solutions; and (3) unsteady aerodynamics changes the stable regions of trim points obviously. Furthermore, the dynamic responses of the aircraft to elevator deflections are inspected It is shown that the unsteady aerodynamics is beneficial to dynamic stability for the present aircraft. Finally, the effects of unsteady aerodynamics on the post-stall maneuverability are analyzed by numerical simulation.     

Biomimetic propulsion under random heaving conditions,using active pitch control

Marine mammals travel long distances by utilizing and transforming wave energy to thrust through proper control of their caudal fin. On the other hand, manmade ships traveling in a wavy sea store large amounts of wave energy in the form of kinetic energy for heaving, pitching, rolling and other ship motions. A natural way to extract this energy and transform it to useful propulsive thrust is by using a biomimetic wing. The aim of this paper is to show how an actively pitched biomimetic wing could achieve this goal when it performs a random heaving motion. More specifically, we consider a biomimetic wing traveling with a given translational velocity in an infinitely extended fluid and performing a random heaving motion with a given energy spectrum which corresponds to a given sea state. A formula is invented by which the instantaneous pitch angle of the wing is determined using the heaving data of the current and past time steps. Simulations are then performed for a biomimetic wing at different heave energy spectra, using an indirect Source-Doublet 3-D–BEM, together with a time stepping algorithm capable to track the random motion of the wing. A nonlinear pressure type Kutta condition is applied at the trailing edge of the wing. With a mollifier-based filtering technique, the 3-D unsteady rollup pattern created by the random motion of the wing is calculated without any simplifying assumptions regarding its geometry. Calculated unsteady forces, moments and useful power, show that the proposed active pitch control always results in thrust producing motions, with significant propulsive power production and considerable beneficial stabilizing action to ship motions. Calculation of the power required to set the pitch angle prove it to be a very small percentage of the useful power and thus making the practical application of the device very tractable.     

Reduced order nonlinear aeroelasticity of swept composite wings using compressible indicial unsteady aerodynamics

Nonlinear dynamic aeroelasticity of composite wings in compressible flows is investigated. To provide a reasonable model for the problem, the composite wing is modeled as a thin walled beam (TWB) with circumferentially asymmetric stiffness layup configuration. The structural model considers nonlinear strain displacement relations and a number of non-classical effects, such as transverse shear and warping inhibition. Geometrically nonlinear terms of up to third order are retained in the formulation. Unsteady aerodynamic loads are calculated according to a compressible model, described by indicial function approximations in the time domain. The aeroelastic system of equations is augmented by the differential equations governing the aerodynamics lag states to derive the final explicit form of the coupled fluid-structure equations of motion. The final nonlinear governing aeroelastic system of equations is solved using the eigenvectors of the linear structural equations of motion to approximate the spatial variation of the corresponding degrees of freedom in the Ritz solution method. Direct time integrations of the nonlinear equations of motion representing the full aeroelastic system are conducted using the well-known Runge–Kutta method. A comprehensive insight is provided over the effect of parameters such as the lamination fiber angle and the sweep angle on the stability margins and the limit cycle oscillation behavior of the system. Integration of the interpolation method employed for the evaluation of compressible indicial functions at any Mach number in the subsonic compressible range to the derivation process of the third order nonlinear aeroelastic system of equations based on TWB theory is done for the first time. Results show that flutter speeds obtained by the incompressible unsteady aerodynamics are not conservative and as the backward sweep angle of the wing is increased, post-flutter aeroelastic response of the wing becomes more well-behaved.     

Low-order phenomenological modeling of leading-edge vortex formation

A low-order point vortex model for the two-dimensional unsteady aerodynamics of a flat plate wing section is developed. A vortex is released from both the trailing and leading edges of the flat plate, and the strength of each is determined by enforcing the Kutta condition at the edges. The strength of a vortex is frozen when it reaches an extremum, and a new vortex is released from the corresponding edge. The motion of variable-strength vortices is computed in one of two ways. In the first approach, the Brown–Michael equation is used in order to ensure that no spurious force is generated by the branch cut associated with each vortex. In the second approach, we propose a new evolution equation for a vortex by equating the rate of change of its impulse with that of an equivalent surrogate vortex with identical properties but constant strength. This impulse matching approach leads to a model that admits more general criteria for shedding, since the variable-strength vortex can be exchanged for its constant-strength surrogate at any instant. We show that the results of the new model, when applied to a pitching or perching plate, agree better with experiments and high-fidelity simulations than the Brown–Michael model, using fewer than ten degrees of freedom. We also assess the model performance on the impulsive start of a flat plate at various angles of attack. Current limitations of the model and extensions to more general unsteady aerodynamic problems are discussed.     

两种椭圆翼型高速气动特性实验研究

新概念旋转机翼飞机的主机翼既能高速旋转作为旋翼,又可锁定作为固定翼,所以只能使用特殊的前后对称翼型。针对主机翼翼型的这一特殊要求,对16％相对厚度,相对弯度分别为0％和3％的两种椭圆翼型的高速气动特性进行了风洞实验研究,试验分别在中国空气动力研究发展中心FL-21风洞和荷兰代尔夫特大学TST-27风洞进行,采用表面测压和尾排型阻测量技术。试验结果的对比分析表明,有弯度椭圆翼型的升力和力矩特性优于无弯度椭圆翼型,而阻力特性和最大升阻比劣于无弯度椭圆翼型。试验结果为旋转机翼飞机主机翼翼型的选取提供了参考。