模型昆虫翼作非定常运动时的气动力特性  被引量:36

AERODYNAMIC PROPERTIES OF A WING PERFORMING UNSTEADY ROTAIONAL MOTIONS

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作  者:兰世隆[1] 孙茂[1] 

机构地区:[1]北京航空航天大学流体力学研究所,北京100083

出  处:《力学学报》2001年第2期173-182,共10页Chinese Journal of Theoretical and Applied Mechanics

摘  要:基于Navier-Stokes方程的数值解,研究了一模型昆虫翼在小雷诺数(Re=100)下作非定常运动时的气动力特性,这些运动包括:翼启动后的常速转动,快速加、减速转动,常速转动中快速上仰(模拟昆虫翼的上挥或下拍、翻转等运动)有如下结果:在小雷诺数下,模型昆虫翼以大攻角(α=35°)作常速转动运动时,由于失速涡不脱落,可产生较大的升为系数。其机理是:翼转动时,翼尖附近(该处线速度大)上翼面压强比翼根附近(该处线速度小)的小得多,因而存在展向压强梯度,同时存在着沿展向的离心力,此展向压强梯度和离心力导致的展向流动在失速涡的轴向方向,其可避免失速涡脱落。模型昆虫翼在快速加、减速转动和快速上仰运动中,虽然雷诺数小,但由于在短时间内产生了大涡量,也可产生十分大的气动力,例如在快速上仰运动中,升力系数可大于10。The aerodynamic forces and flow structures of a wing of relatively small aspect ratio in some unsteady rotational motions at low Reynolds number (Re = 100) are studied by numerically solving the Navier-Stokes equations. These motions include wing in constant-speed rotation after a fast start, wing accelerating and decelerating from one rotational speed to another, and wing rapidly pitching-up in constant-speed rotation. When a wing performing constant-speed rotation at small Reynolds number after started from rest at large angle of attack (α = 35°), α large lift coefficient can be maintained. The mechanism for the large lift coefficient is that for a rotating wing, the variation of the relative velocity along the wing-span causes a pressure gradient, centrifugal force also exists and hence a spanwise flow which can prevent the dynamic stall vortex from shedding. When a wing rapidly accelerating or decelerating from one rotational speed to another, or rapidly pitching-up during constant-speed rotation, even if the aspect ratio of the wing is small and the flow Reynolds number is low, large aerodynamic force can be obtained. During these rapid unsteady motions, new layers of strong vorticity are formed near the wing surfaces in very short time, resulting large time rate of change of the fluid impulse which is responsible for the generation of large aerodynamic force.

关 键 词:低雷诺数 翼型 非定常运动 气动力特性 微型飞机 模型昆虫翼 

分 类 号:V211.4[航空宇航科学与技术—航空宇航推进理论与工程]

 

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