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扑动而形成非定常气动现象是扑翼飞行过程中产生高升力的主要原因。本文以Ellington实验的鹰蛾翅膀为原形,设计扑翼实验及数值计算模型。通过压差传感器对翅膀模型上翼面固定位置进行测压,分析前缘涡的产生及脱落情况(考虑动压效应)。测量上下翼面固定位置处的压差,揭示扑翼飞行中产生高升力的主要原因。利用烟风洞观察扑翼模型周围流场结构及特殊涡产生变化情况。另外,根据Ellington提供的升力关系式估算了扑翼模型在一个周期内的平均升力。最后,基于三维欧拉方程对扑翼飞行气动特性进行数值模拟,计算结果与实验吻合良好。 相似文献
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柔性扑翼的气动特性研究 总被引:6,自引:0,他引:6
以往扑翼的气动力计算研究都很少考虑扑翼的柔性,而在鸟的扑翼动作中,在外加气动力和鸟自身的扑动力作用下,扑翼的柔性变形相当大。本文在原有匀速刚性模型的基础上,提出考虑了扑翼扑动速率变化和形状变化的扑翼分析模型,使之更接近鸟翼柔性扑动真实情况。通过计算分析气动特性发现,控制适当的话,柔性变形能大大改善扑翼的气动性能。本文通过模拟鸟扑翼的柔性运动,计算了时柔性扑翼气动力以及平均升力系数和平均推力系数随着扑动角、倾斜角等参数变化的情况,从而从气动的角度解释了为什么鸟在不同的飞行阶段扑翼规律各不相同,并为柔性扑翼飞行器的设计提供了理论依据。 相似文献
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扑翼柔性及其对气动特性的影响 总被引:4,自引:1,他引:3
以往对扑翼气动特性的研究基本上都是基于简单的匀速刚性模型,但是通过大量观察不同飞鸟的扑翼动作发现,该模型与鸟翼的实际扑动还有很大差别。鸟翼不但上扑段和下扑段所需时间不同,而且在扑动过程中,鸟翼的形状无论沿弦向或展向都存在着相当大的柔性变形。本文在原有匀速刚性模型的基础上,加入了扑动速率变化和形状变化的影响,得出新的变速柔性扑翼分析模型,使之更接近鸟翼柔性扑动的真实情况。通过对比计算发现,柔性变形对扑翼的升力与推力都有着显著影响,如果控制得当,柔性变形能大大改善扑翼的气动性能。 相似文献
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一种用于研究鹰蛾悬停飞行的扑翼实验装置 总被引:1,自引:0,他引:1
研制了一套新型的能够在空气中模拟鹰蛾悬停飞行的扑翼模型实验装置。装置由模型翼面和主体、舵机驱动单元、运动控制与检测、测力天平和采集系统等五部分构成。模型在计算机的控制下按照鹰蛾悬停飞行的活体观测数据完成扑翼运动。与此同时,系统采集得到扑翼的实际运动曲线以及模型所受到的非定常气动力。实验结果表明,模型扑翼运动能很好地复现鹰蛾悬停飞行的动态过程;所测得的气动升力与鹰蛾的悬停条件相一致;由模型实验的升阻力数据所得的挥拍面前倾角也与活体观测结果相吻合。该模拟实验装置运动调节灵活,执行便捷,操控可靠,且能够测量空气中的微小非定常气动力,这为进一步深入研究扑翼运动的机理提供了方便的手段。 相似文献
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两串列扑翼的相位差对平均推力影响机理的实验研究 总被引:1,自引:0,他引:1
在一个低雷诺数的循环水洞中,实验研究了前后翅翼之间的相位差对两串列扑翼平均推力的影响.利用一个三分量的Kistler 压力传感器来测量扑翼的瞬时力;利用一个数字粒子测速仪系统(TSI DPIV) 来测量扑翼的前缘涡以及其周围的流场. 当相位差从0° 增加到360°,前翅的平均推力随着相位差正弦变化;前翅平均推力的增加是由于后翅的前缘涡和滞止区域增加了前翅的有效攻角. 后翅平均推力曲线有一个明显的V 字形低谷.低谷处较小的平均推力是由于前翅的脱落涡抑制了后翅前缘涡的形成并且减小了其有效攻角.当间距为0.5倍弦长相位差约为290°时,前后翅翼平均推力系数的合值能达到最大值0.667,明显大于两倍的单翼平均推力系数(2×0.255). 相似文献
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膜扑翼飞行器的变形研究 总被引:1,自引:0,他引:1
最近昆虫翼的变形成了研究热点,而扑翼飞行器的变形力学研究却几乎无人问津.然而,无论昆虫、鸟类还是扑翼飞行器在飞行时,翼的变形都是存在的,要精确计算翼扑动产生的气动力,必须考虑其变形.本文比较了导致变形产生的膜扑翼飞行器的惯性力和气动力在一个周期中的变化情况,发现它们的峰值比值为2左右,然后提出了在随体坐标系中的固支边界条件,采用有限元法计算了惯性力和气动力分别对变形的影响,发现扑翼飞行器的气动力对变形的影响是不可忽略的重要因素,而惯性力与气动力的合力引起的最大正变形发生在下扑初始阶段,最大负变形发生在上扑初始阶段.本文为扑翼飞行器的设计提供了力学分析基础. 相似文献
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小型飞行器空气动力学 总被引:5,自引:0,他引:5
对小型飞行器设计中涉及的空
气动力学问题进行了综述.描述了雷诺数和展弦比对固定翼飞行器的设计以及飞行
性能的影响.在低雷诺数飞行范围,翼型上边界层的特性对飞行器的设计尤为关键.
本文讨论了大量有关层流边界层(包括层流分离泡影响)的实验,作为例子,列举了几
个此飞行雷诺数范围的小型低空无人驾驶飞行器(UAVs).此外,对扑动翼推进的理论
模型进行了简述;其范围涵盖了早期的准定常附着流模型,以及后来计及非定常尾涡、
流动分离以及气动弹性等效应的模型.文中还介绍了那些与理论互补并最终导致扑
翼机设计成功的实验. 相似文献
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昆虫飞行的高升力机理 总被引:30,自引:0,他引:30
对近年来关于昆虫产生非定常高升力的研究进行了综述和归纳.这方面的工作对生物学研究和微型飞行器等微型机械的仿生设计有重要意义.研究表明:果蝇等昆虫翅膀的拍动运动可产生很大的非定常升力,其平均值是定常值的2~3倍,足够平衡昆虫的重量,并有较大的富余用于机动飞行;产生高升力有三个因素:一是拍动开始阶段翅的快速加速运动,二是拍动中的不失速机制,三是拍动结束阶段翅的快速上仰运动.人们从能耗的角度考察了这些非定常高升力机制的正确性和可行性.当作悬停飞行的果蝇用以上机制产生平衡其重量的升力时,其比功率(支持单位身体质量所需的功率)约为29W/kg, 生化/机械效率约为17%. 这些值与人们基于对昆虫肌肉力学特性的研究所预估的值接近.果蝇前飞时,其比功率随速度变化的曲线是一J形曲线,而不是象飞机或鸟的那样是一U形曲线;这与人们基于昆虫新陈代谢率的测量数据所推断的结果一致.对于蜻蜒等(功能上)有前、后两对翅膀的昆虫,有以下初步结果:翅的下拍主要产生升力,上挥主要产生推力;下拍时的平均升力系数可达2~3,十分大,上挥时的平均推力系数可达1~2, 也很大,它们主要由非定常效应产生;前、后翅的相互干扰并未起增大升力和推力的作用,反而有一定的不利作用. 相似文献
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Winged animals such as insects are capable of flying and surviving in an unsteady and unpredictable aerial environment. They generate and control aerodynamic forces by flapping their flexible wings. While the dynamic shape changes of their flapping wings are known to enhance the efficiency of their flight, they can also affect the stability of a flapping wing flyer under unpredictable disturbances by responding to the sudden changes of aerodynamic forces on the wing. In order to test the hypothesis, the gust response of flexible flapping wings is investigated numerically with a specific focus on the passive maintenance of aerodynamic forces by the wing flexibility. The computational model is based on a dynamic flight simulator that can incorporate the realistic morphology, the kinematics, the structural dynamics, the aerodynamics and the fluid–structure interactions of a hovering hawkmoth. The longitudinal gusts are imposed against the tethered model of a hovering hawkmoth with flexible flapping wings. It is found that the aerodynamic forces on the flapping wings are affected by the gust, because of the increase or decrease in relative wingtip velocity or kinematic angle of attack. The passive shape change of flexible wings can, however, reduce the changes in the magnitude and direction of aerodynamic forces by the gusts from various directions, except for the downward gust. Such adaptive response of the flexible structure to stabilise the attitude can be classified into the mechanical feedback, which works passively with minimal delay, and is of great importance to the design of bio-inspired flapping wings for micro-air vehicles. 相似文献
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Effects of unsteady deformation of a flapping model insect wing on its aerodynamic force production are studied by solving the Navier-Stokes equations on a dynamically deforming grid.Aerodynamic forces on the flapping wing are not much affected by considerable twist,but affected by camber deformation.The effect of combined camber and twist deformation is similar to that of camber deformation.With a deformation of 6% camber and 20°twist(typical values observed for wings of many insects),lift is increased bv 10%~20%and lift-to-drag ratio by around 10%compared with the case of a rigid flat-plate wing.As a result.the deformation can increase the maximum lift coefficient of an insect.and reduce its power requirement for flight.For example,for a hovering bumblebee with dynamically deforming wings(6?mber and 20°twist),aerodynamic power required is reduced by about 16%compared with the case of rigid wings. 相似文献
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We use a potential flow solver to investigate the aerodynamic aspects of flapping flights in enclosed spaces. The enclosure effects are simulated by the method of images. Our study complements previous aerodynamic analyses which considered only the near-ground flight. The present results show that flying in the proximity of an enclosure affects the aerodynamic performance of flapping wings in terms of lift and thrust generation and power consumption. It leads to higher flight efficiency and more than 5% increase of the generation of lift and thrust. 相似文献
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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