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1.
三角翼动态大迎角气动力特性数值分析研究   总被引:1,自引:0,他引:1  
采用数值计算方法,对三角翼从 0°上仰至 90°的动态流场和气动力特性进行了计算,并对俯仰角速度对三角翼流场和气动力特性的影响进行了计算分析。给出了三角翼纵向动态情况下的气动力系数变化,特别是大迎角横侧力矩系数的变化特征。结果表明,随着机翼俯仰角速度的提高,前缘分离涡破裂位置相对滞后,机翼升力和阻力系数明显增加,机翼抵抗旋涡非对称破裂的能力明显增强。  相似文献   

2.
采用“单一叶片振动方法”代替传统的“全部叶片振动方法”,用线性化的方法推导出计算振动叶片非定常气动力(引起叶片弯曲振动)及力矩(引起叶片扭转振动)方程。通过输入叶型及气流参数,它可以方便有效地估计出作用在振动叶片上的非定常气动力和力矩,以及振动叶片不稳定工况发生的条件和范围。并在氟里昂超音速风洞上进行了实验测量,结果表明,理论计算结果与实验测试结果符合较好。  相似文献   

3.
采用数值计算方法对亚音速三角翼纵向及带有小侧滑情况下的流场结构和气动力特性进行了计算。文中给出了三角翼大迎角纵向情况下气动力、机翼前缘分离涡轴线位置和旋涡破裂位置随迎角的变化规律,以及带有横侧小扰动和小侧滑情况下流场结构的非对称性对气动力的影响。计算结果表明与实验结果符合较好。  相似文献   

4.
可变形儒可夫斯基翼型非定常气动力的研究   总被引:1,自引:0,他引:1  
对于翼面变形法向运动速度远小于来流速度的儒可夫斯基机翼,将解析解和离散涡方法相结合计算变形机翼的流场及非定常气动力,较详细地分析了变形机翼升力系数的准定常计算方法的误差来源,并给出修正方法.计算结果显示脱落涡尾迹对升力系数和机翼绕流环量的影响很小,变形机翼升力系数准定常计算方法的误差丰要来源于流体非定常运动引起的虚拟质量力,该非定常附加升力仅与当前时刻飞行姿态及翼犁形状和变形速率有关,与具体的变形历史过程无关,变形机翼的升力近似等于准定常计算结果叠加上相应的虚拟质量力.  相似文献   

5.

The vast majority of research works on low aspect ratio rotating wings report that, at high angle of attack, the leading edge vortex that forms on the upper surface of the wing is stable. This ‘trick’ is used by insects and auto-rotating seeds, for example, to achieve the desirable amount of lift. Yet, a few experimental studies suggest that leading edge vortices might be unstable under similar, low Rossby number, conditions. While it is unclear what causes vortex shedding in these studies, the present communication explores the sensitivity of leading edge vortex attachment to perturbations of the rotating speed and demonstrates that shedding can be triggered even for very small perturbations, corresponding to wing tip displacements lower than 1% of the wing chord.

  相似文献   

6.
This paper documents the elastic deformations and corresponding aerodynamic coefficients of flexible wings used for micro air vehicles (MAVs). These low-aspect ratio wings, developed and fabricated at the University of Florida, incorporate an elastic latex membrane skin covering a thin carbon fiber skeleton. The wings were tested in a unique low-speed wind tunnel facility integrating a visual image correlation (VIC) system with a six-component strain gauge sting balance. Model characteristics are presented, along with the appropriate specimen preparation techniques and wind tunnel instrumentation. The static response characteristics, including full-field displacements and plane strain measurements, for three distinct MAV wing designs are presented. The full-field deformation results show how passive wing flexibility preferably affects aerodynamic performance when compared to a rigid model of similar geometry.  相似文献   

7.
徐国武  白鹏 《力学季刊》2012,(2):165-173
可变形飞行器的优越性,使其成为近年来研究者关注的热点。当前对于可变形飞行器气动方面的研究工作主要集中于采用数值模拟或风洞实验,开展可变形飞行器气动布局概念和不同变形模态气动特性研究,而关于连续变形过程中非定常气动特性的研究则很少,几为空白。本文在无粘不可压(Ma=0.2)流场中,数值模拟了儒可夫斯基翼型连续改变厚度、弯度所引起的气动特性变化,分析了不同变形幅度、变形速度以及变形加速度对非定常升力系数的影响情况,这也为以后的三维数值模拟提供了基础。  相似文献   

8.
The paper is aimed at reviewing and adding some new results to our recent work on a force theory for viscous compressible flows around a finite body. It has been proposed to analyze aerodynamic forces directly in terms of fluid elements of nonzero vorticity and density gradient. Let ρ denote the density, u the velocity, and ω the vorticity. It is demonstrated that for largely separated flows about bluff bodies, there are two major source elements: R e(x) =−?u 2∇ρ·∇ϕ and V e(x) =−u×ω·∇ϕ, where ϕ is an acyclic potential, generated by the solid body moving with unit velocity in the negative direction of the force considered. In particular, under mild conditions, the (unique) choice of ϕ enforces that the elements R e(x) and V e(x) decay rapidly away from the body. Four kinds of finite body are considered: a circular cylinder, a sphere, a hemi sphere-cylinder, and a delta wing of elliptic section—all in transonic-to-supersonic regimes. From an extensive numerical study carried out for these bodies, it is found that these two elements contribute to 95% or more of the total drag or lift for all the cases under consideration. Moreover, R e(x) due to density gradient becomes progressively important relative to V e(x) due to vorticity as the Mach number increases. The present method of force analysis enables effective analysis and assessment of relative importance of aerodynamics forces, contributed from individual flow structures. The analysis could therefore be very much useful in view of the rapid growth in numerical fluid dynamics; detailed (either local or global) flow information is often available. The paper is dedicated to Sir James Lighthill in honor of his great contributions to aeronautics on the occasion of the publication of his collected works. Received 3 January 1997 and accepted 11 April 1997  相似文献   

9.
应用有限体积方法求解三维可压缩雷诺平均N-S方程,计算了某型巡航导弹的静、动态绕流流场和空气动力特性.湍流模型应用修正后的B-L代数湍流模型.以细长旋成体绕流流场为例进行数值计算,并和实验数据相比较,验证了本文方法的可靠性,在此基础上,开展了某型巡航导弹绕不同转轴和以不同频率进行俯仰振动的非定常气动力迟滞特性研究.计算结果表明,当导弹作快速俯仰振动时,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.并且,导弹的非定常气动力迟滞特性随振动频率的增大变化明显,且气动力迟滞曲线随着振动轴位置的变化而变化.  相似文献   

10.
对于翼面变形速度远小于来流速度情况下的儒可夫斯翼型亚音速绕流问题,通过仿射变换将可压缩流动转换成不可压缩流动,将解析解和离散涡方法相结合计算变形机翼的不可压缩流动速度场,再利用逆变换得到变形机翼的亚音速流动速度场,进而分析非定常气动力特性,建立变形机翼的准定常升力系数和非定常附加升力系数在可压缩和不可压缩两种状态下的简单近似对应关系。计算结果显示变形机翼的非定常气动升力近似等于准定常计算结果叠加上虚拟质量力导致的非定常附加升力,该非定常附加升力随翼型变形速率呈线性关系,由机翼当前时刻飞行姿态、翼型及其变形速率确定,与具体变形历史过程无关。低来流马赫数时虚拟质量力导致的非定常效应显著,高亚音速流动时准定常升力起主导作用。同时还分析了不同马赫数下机翼往复变形过程中升力的变化特性,指出尽管高亚音速变形机翼的气动升力近似等于准定常气动升力,但不能忽视非定常附加升力的影响,非定常附加升力将导致完成往复变形需要外界输入正比于Ma∞/[(1-Ma2∞)]的功。  相似文献   

11.
主动控制翼板抑制悬索桥颤振的研究   总被引:1,自引:0,他引:1  
主动控制翼板是一种新型桥梁气动措施。本文基于非定常气动力理论,推演了安装主动控制翼板后作用在整个桥梁主梁单位长度上气动力表达式,从增加系统扭转阻尼的角度,研究了翼板主动扭转振动参数的选取。在此基础上,对某大跨悬索桥方案进行了二自由度颤振分析,结果表明:合理选取翼板的主动扭转振动参数,主动控制翼板能够有效地提高该桥的颤振稳定性。  相似文献   

12.
Graziani  Giorgio  Bassanini  Piero 《Meccanica》2002,37(3):283-303
The force (drag and lift) exerted on a body moving in a viscous fluid is expressed via the free and bound vorticity moments, and the role of vortex shedding is discussed. The formulation encompasses classical, inviscid flows, and leads to efficient computational methods. Numerical results for a few prototype flows are presented.  相似文献   

13.
A formula relating the forces exerted on a three-dimensional body to the motion of a vortex and source system simulating that body is derived for an unsteady vortex separation flow of an ideal incompressible fluid. The shape of the body can vary with time. In the case of steady-state homogeneous flow past an airfoil the formula obtained coincides with the Joukovski formula.  相似文献   

14.
The supersonic flow past a bent delta wing and its aerodynamic characteristics, both local and integral, are studied using approximate analytic estimates and numerical calculations. The flow regimes with the shock attached to the leading edges are considered. It is established that at M = 4–6 and angles of attack as high as 6° the lift-drag ratio of the wing can be increased by 10% by deflecting the wing nose downwards. This is confirmed by the results obtained earlier in the hypersonic thin-shock-layer approximation. The effect is also obtained in calculations made within the framework of the Navier-Stokes equations.  相似文献   

15.
The present paper evaluates two unsteady transition modelling approaches: the prescribed unsteady intermittency method PUIM, developed at Cambridge University and the dynamic unsteady intermittency method developed at Ghent University. The methods are validated against experimental data for the N3-60 steam turbine stator profile for steady and for unsteady inlet flow conditions. The characteristic features of the test case are moderately high Reynolds number and high inlet turbulence intensity, which causes bypass transition. The tested models rely both on the intermittency parameter and are unsteady approaches. In the prescribed method, the time-dependent intermittency distribution is obtained from integral relations. In the dynamic method, the intermittency distribution follows from time-dependent differential equations. For unsteady computations, self-similar wake profiles are prescribed at the inlet of the computational domain. Joint validation of the prescribed and the dynamic unsteady intermittency models against experimental data shows that both methods are able to reproduce the global features of the periodical evolution of the boundary layer under the influence of a periodically impinging wake. The overall quality of the dynamic method is better than that of the prescribed method.  相似文献   

16.
Unsteady motion of a Maxwellian fluid droplet, which arises in a quiescent Maxwellian medium under the action of monotonic and periodic forces, is considered. In the initial period of time smaller than the relaxation time, the droplet is affected by elastic forces on the part of the fluid; moreover, the droplet itself is a viscoelastic material. A solution of the problem in the first approximation is found. The dependence of the amplitude of droplet velocity and the shift of the phase of oscillations on the relaxation time of the external and internal media and also on the frequency of oscillations of the driving force is analyzed. The passage to the limit in terms of density and viscosity of the internal medium is performed.__________Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 4, pp. 55–65, July–August, 2005.  相似文献   

17.
G. N. Dudin 《Fluid Dynamics》2005,40(6):973-984
The flow over a planar low-aspect-ratio delta wing is considered in the strong viscous-inviscid interaction regime. The study is carried out for Newtonian passage to limit, when the adiabatic exponent tends to unity, while the Mach and Reynolds numbers increase without bound. For the flow over a cold wing, an analytical expression for the coordinate of supercritical-to-subcritical transition in the boundary layer is derived. The aspect ratios for which the flow in the three-dimensional boundary layer is subcritical over the entire wing are derived. The approximate formula for the transition coordinate is compared with the results of a numerical solution of the system of differential equations in the case in which the Prandtl number is equal to unity.  相似文献   

18.
The results of experimental investigations of the multiple static hysteresis of the aerodynamic characteristics of a rectangular high-aspect-ratio wing are presented. Schematic wing-flow structure patterns, time dependences of the coefficients c y(t), m z(t), and m x(t) and their frequency spectra obtained for a fixed model are given for different boundaries of the hysteresis domain. The time dependences of aerodynamic forces and moments are analyzed at angles of incidence at which sharp changes are observed. It is shown that the static hysteresis can be described by a mathematical model used in catastrophe theory.  相似文献   

19.
An experimental investigation of freely rising spherical bubbles through a quiescent liquid is presented. The objective of the experiments is to examine the validity of a recently proposed history force expression for clean, spherical bubbles at finite Reynolds number (Mei et al. 1994). Excellent agreement between the measured and predicted bubble trajectory is obtained when using the proposed history force expression; the data presented herein thus provide an indirect validation of the history force expression. The range of Reynolds number and Weber Number based on the terminal velocity are 13 to 212 and 0.03 to 0.69, respectively. The history force expression is only applicable when the quiescent liquid is free of contaminants. Otherwise, both the steady and unsteady forces are difficult to predict because the liquid/ vapor interface is partially immobilized.Department of Mechanical Engineering  相似文献   

20.
Compared with the traditional train, the operational speed of the high-speed train has largely improved, and the dynamic environment of the train has changed from one of mechanical domination to one of aerodynamic domination. The aerodynamic problem has become the key technological challenge of high-speed trains and significantly affects the economy, environment, safety, and comfort. In this paper, the relationships among the aerodynamic design principle, aerodynamic performance indexes, and design variables are first studied, and the research methods of train aerodynamics are proposed, including numerical simulation, a reduced-scale test, and a full-scale test. Technological schemes of train aerodynamics involve the optimization design of the streamlined head and the smooth design of the body surface. Optimization design of the streamlined head includes conception design, project design, numerical simulation, and a reduced-scale test. Smooth design of the body surface is mainly used for the key parts, such as electric-current collecting system, wheel truck compartment, and windshield. The aerodynamic design method established in this paper has been successfully applied to various high-speed trains (CRH380A, CRH380AM, CRH6, CRH2G, and the Standard electric multiple unit (EMU)) that have met expected design objectives. The research results can provide an effective guideline for the aerodynamic design of high-speed trains.  相似文献   

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