Vortex filamentation and fragmentation phenomena in flapping motion and effect of aspect ratio and frequency on global strain, rotation, and enstrophy

IF 1.5 4区 工程技术 Q2 ENGINEERING, AEROSPACE
Srikanth Goli, Arnab Roy, Subhransu Roy
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引用次数: 4

Abstract

In the present study, flow field around rigid flat plate wings executing main flapping motion has been studied using phase-locked two-dimensional particle image velocimetry measurements. Experiments have been conducted in water as a fluid medium for an asymmetric upper–lower stroke single degree of freedom main flapping motion. Two different aspect ratio (1.5 and 1.0) rectangular wings at 1.5 and 2.0 Hz flapping frequency in hovering flight mode (advance ratio, J = 0), zero wing pitch angle, and chord-based Reynolds number of the order of 104 have been studied. Velocity field and vorticity field with λ2 criterion information have been obtained for the complete stroke in great detail to reveal the minute aspects of flow dynamics. The flow features during the downstroke and upstroke have been observed to be consistent for all four cases investigated. The predominant characteristic of the flow during downstroke and upstroke has been referred to as vortex filamentation and fragmentation phenomena. Quantities such as circulation, rate of strain, rate of rotation, and enstrophy have been studied to identity the effect of minor change in aspect ratio and flapping frequency. It is found that for higher aspect ratio wing hyperbolic behavior is predominant except for end of downstroke and beginning of upstroke where elliptic behavior is observed. For lower aspect ratio, wing elliptic behavior is predominant except for end of upstroke and beginning of downstroke where hyperbolic behavior is seen. The hyperbolic behavior became stronger at higher frequency. From enstrophy distribution it is evident that higher frequencies play a more dominant role than aspect ratio in determining the budget.
扑翼运动中的旋涡丝状和碎裂现象以及纵横比和频率对整体应变、旋转和自养的影响
在本研究中,使用锁相二维粒子图像测速仪测量了执行主要扑动的刚性平板机翼周围的流场。已经在水作为流体介质中进行了不对称上下行程单自由度主扑动的实验。两个不同的纵横比(1.5和1.0)矩形机翼,分别为1.5和2.0 Hz悬停飞行模式下的扑动频率(推进比,J = 0)、零机翼桨距角和104量级的基于弦的雷诺数。获得了完整行程的速度场和涡度场的详细信息,揭示了流动动力学的微观方面。已经观察到,在所研究的所有四种情况下,下行和上行期间的流动特征是一致的。在下行和上行过程中,气流的主要特征被称为涡流成丝和碎裂现象。已经研究了循环、应变率、旋转率和自养等量,以确定纵横比和拍打频率的微小变化的影响。研究发现,对于高展弦比机翼,除了下行程结束和上行程开始时观察到椭圆行为外,双曲行为是主要的。对于较低的展弦比,除了上行程结束和下行程开始时可以看到双曲线行为外,机翼的椭圆行为是主要的。双曲线行为在更高的频率下变得更强。从enstrophy分布可以明显看出,在决定预算时,较高的频率比纵横比起着更重要的作用。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
CiteScore
3.00
自引率
7.10%
发文量
13
审稿时长
>12 weeks
期刊介绍: The role of the International Journal of Micro Air Vehicles is to provide the scientific and engineering community with a peer-reviewed open access journal dedicated to publishing high-quality technical articles summarizing both fundamental and applied research in the area of micro air vehicles.
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