【作者】 宋书恒；

【导师】 朱国林；

【作者基本信息】 中国空气动力研究与发展中心 ， 流体力学， 2008， 博士

【摘要】 微型飞行器(Micro Air Vehicles或Micro Aerial Vehicles,简称MAVs)是由美国DARPA(Defense Advanced Research Projects Agency)在二十世纪九十年代提出的一种新概念飞行器,它是一种融合了MEMS(Micro-electromechanical Systems)等多种高新技术于一体的集成化智能微型系统。微型飞行器在军事和民用方面具有十分广阔的应用前景和使用价值。微型飞行器的研制,必然要求其相关的空气动力学研究起到先导的作用。其低雷诺数空气动力学特性问题,如翼型低雷诺数绕流、小展弦比机翼的低雷诺数气动力特性以及扑翼的非定常气动力特性等方面都是微型飞行器研发对空气动力学领域提出的重点研究项目,这些研究将为微型飞行器的设计和发展奠定基础。本文围绕微型飞行器所涉及的上述几方面的空气动力学问题展开了相应的数值模拟研究。论文首先回顾了微型飞行器的提出、产生的背景以及目前国内外的研究现状,较全面阐述了微型飞行器的基本特征、应用前景和分类,对微型飞行器所蕴涵的空气动力学问题进行了系统总结和分析,并指出开展其研究对微型飞行器发展的重要意义。针对微型飞行器相关气动力特性的数值模拟,论文发展了与之相适应的数值模拟方法,主要包括流体力学的控制方程、空间离散、时间离散、隐式求解方法、边界条件、动网格技术的应用以及湍流模型等方面。基于数值方法本文建立了一套计算软件系统,通过对基本算例的求解,验证了该软件系统的可靠性和有效性,为数值分析微型飞行器相关气动力特性提供了数值模拟的工具。采用本文建立的计算软件,论文首先开展了翼型低雷诺数范围内的气动力特性研究,数值模拟了翼型低雷诺数层流流动的非定常分离现象,证实了其分离结构是一系列旋涡的非定常对并、融合、移动和脱落的复杂过程,时间平均的数值模拟结果与实验结果之间较好的一致性表明了非定常的大尺度分离结构是影响翼型低雷诺数气动力特性的一个主导因素。同时首次数值模拟了较大弯度翼型在小攻角时的非定常流场,在该条件下,得到了一种新的非定常层流分离结构,深入探讨了其非定常流动分离结构随攻角的演变规律及其对翼型气动力的影响。为了满足受尺寸限制的固定翼微型飞行器气动布局的设计需求,论文数值模拟了小展弦比机翼的低雷诺数流场,研究了展弦比、弯度、攻角、机翼形状等对小展弦比机翼气动性能的影响,首次重点分析了小展弦比机翼流场中翼尖涡对机翼气动力和流动分离的作用、翼尖涡的涡态结构、尾迹区翼尖涡的强度及发展变化规律。扑翼作为一种高效的推进方式为微型飞行器的发展提供了另外一种途径。论文对几种扑翼的非定常气动特性进行了数值模拟,系统研究了扑翼的非定常气动力和流场,考察了频率、振幅、相位差等关键因素对扑翼气动力的影响,并对各种扑翼的推进效率作了比较。为了考虑三维效应,数值计算了三维扑翼的非定常流场,较全面分析了展弦比、频率等对三维扑翼气动力、表面流态、动态压力分布的影响规律,并研究了不同情况下三维扑翼流场中的翼尖涡现象。更多还原

【Abstract】 MAVs(Micro Air Vehicles or Micro Aerial Vehicles), a new-concept vehicle proposed by Defence Advanced Research Projects Agency(DARPA) in the United States in 1990 s, is a kind of smart integrated micro system which combines multiple high-tech technologies such as Micro-electromechanical Systems(MEMS). It owns a very broad prospect in military and civil aera. Aerodynamic research is always the preceding action for any new vehicle development, so does the MAVs. Many major projects related with low Reynolds number aerodynamic characteristics are very crucial for the development of the MAVs such as low Reynolds number flow of the airfoil, low Reynolds number aerodynamic characteristics of low-aspect-ratio wing and unsteady aerodynamic characteristics of the flapping wing. They will create very fundamental basis for the MAVs design and development. This paper presents some numerical simulation study for several above-mentioned aerodynamic phenomena related with the MAVs.Firstly, background and status of the MAVs development are addressed in the paper. Then, its basic characteristics, application prospect, classification and aerodynamic problem are summarized and analyzed. The significance of performing these researches is also pointed out.To carry out the numerical simulation of aerodynamic characteristics for the MAVs, some numerical simulation methods are developed, mainly including govering equations, spatial discretization, temporal discretization, implicit solver, numerical boundary conditions, dynamic grid technology and turbulence model. A set of computation software system is established in this paper. Its reliability and effectiveness are verified by the solution of some basic examples. So it provides a numerical simulation tool to perform the numerical analysis of the related aerodynamic characteristics for the MAVs.Aerodynamic characteristics research in low Reynolds number range of the airfoil is first performed utilizing the computation software established in this paper. The unsteady separation phenomenon for the low Reynolds number laminar flow of the airfoil is simulated. The simulation results validate the separation is a complex process caused by pairing, merge, motion and shedding of a series of vortex. The better agreement of the time-averaged numerical simulation results with the experimental ones shows that unsteady large-scale separation structure is the predominant factor to affect the low Reynolds number aerodynamic characteristic of the airfoil. Additionally, the unsteady flow field of the airfoil with larger camber is first simulated at smaller angle of attack. A kind of new unsteady laminar flow separation structure is obtained. The evolution relationship of the unsteady flow separation structure with the angle of attack and its effect on aerodynamic performance are deeply discussed.To meet with the aerodynamic configuration design requirements of the MAVs with the fixed wing, low Reynolds number flow field of low-aspect-ratio wing is also numerically simulated. The effect of aspect ratio ,camber, angle of attack and wing shape on the aerodynamic performance of low-aspect-ratio wing is studied. The emphasis on the aerodynamic and flow separation effect of the wingtip vortex, wingtip vortex structure, wingtip vortex strength in wake region and evolution tendency for low-aspect-ratio wing is first addressed.As a kind of high-efficiency propulsion means, the flapping wing provides another development direction for the MAVs. So this paper also carries out the unsteady aerodynamic characteristics simulation of several kinds of flapping wings. The aerodynamic force and the flow field of the flapping wing are systematically studied. The effect of some key parameters, including frequency, amplitude and phase, on the aerodynamic force of the flapping wing is surveyed. The propulsion efficiencies of various flapping wings are compared. For a 3D effect consideration, the unsteady flow field of the 3D flapping wing is numerically calculated. The relationship of aerodynamic force, surface flow state and dynamic pressure distribution for the 3D flapping wing with aspect ratio and frequency is completely analyzed. In addition, the wingtip vortex phenomenon under different conditions is also studied.更多还原