UNSTEADY QUASI-VORTEX-LATTICE METHOD WITH APPLICATIONS TO ANIMAL PROPULSION
UNSTEADY QUASI-VORTEX-LATTICE METHOD WITH APPLICATIONS TO ANIMAL PROPULSION
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DOI：
10.1017/s0022112079002019
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发表时间：
1979-01-01
影响因子：
3.7
通讯作者：
LAN, CE
中科院分区：
文献类型：
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作者：
LAN, CE
在早期的水生动物推进理论研究中，一般采用的不是二维理论，就是大展弦比理论。直到最近，Chopra&Kambe(1977)才将非定常升力面理论和连续加载方法应用于这一问题的研究。鉴于连续加载法很难推广到一般构型，本文提出了一种新的准连续加载法，该方法既适用于一般构型，又具有实际应用的足够精度。该方法是对Lan(1974)定常版本的推广，特别适用于预测简谐运动中的非定常前缘吸力。该方法被应用于通过改变俯仰和升沉运动之间的相位角来计算某些后掠面和矩形平面的推进效率和推力。研究发现，当俯仰轴穿过根弦后缘，折合频率k=0.75时，矩形平板对相角非常敏感，可能产生阻力而不是推力。这些特征并不是模拟月牙形尾巴的扫掠平面所共有的。此外，当俯仰导致升沉运动90°时，俯仰引起的平台倾斜对大部分后掠平台的推进推力有贡献，而对于矩形平台，k=0.75时，平台法向力只产生阻力。研究还发现，对于所考虑的所有平面形式，产生的最大推力并不具有最大效率。然后将该理论应用于蜻蜓空气动力学的研究。结果表明，蜻蜓气动相互作用的串联翼在扑动前俯仰，后翼引导前翼一定的最佳相位角，可以产生高效率的大推力。负责的机制允许后翼从前翼提取尾流能量。
In the early theoretical study of aquatic animal propulsion either the two-dimensional theory or the large aspect-ratio theory has been generally used. Only recently has the unsteady lifting-surface theory with the continuous loading approach been applied to the study of this problem by Chopra & Kambe (1977). Since it is well known that the continuous loading approach is difficult to extend to general configurations, a new quasi-continuous loading method, applicable to general configurations and yet accurate enough for practical applications, is developed in this paper. The method is an extension of the steady version of Lan (1974) and is particularly suitable for predicting the unsteady lead-edge suction during harmonic motion.The method is applied to the calculation of the propulsive efficiency and thrust for some swept and rectangular planforms by varying the phase angles between the pitching and heaving motions. It is found that with the pitching axis passing through the trailing edge of the root chord and the reduced frequency k equal to 0·75 the rectangular planform is quite sensitive in performance to the phase angles and may produce drag instead of thrust. These characteristics are not shared by the swept planforms simulating the lunate tails. In addition, when the pitching leads the heaving motion by 90°, the phase angle for nearly maximum efficiency, the planform inclination caused by pitching contributes to the propulsive thrust over a large portion of the swept planform, while, for the rectangular planform, only drag is produced from the planform normal force at k = 0·75. It is also found that the maximum thrust is not produced with maximum efficiency for all planforms considered. The theory is then applied to the study of dragonfly aerodynamics. It is shown that the aerodynamically interacting tandem wings of the dragonfly can produce high thrust with high efficiency if the pitching is in advance of the flapping and the hindwing leads the forewing with some optimum phase angle. The responsible mechanism allows the hindwing to extract wake energy from the forewing.