By carefully analyzing the flow structure of each bristle on the bristled wings, Wu et al. 11 proposed a Reynolds number based on the gap width between bristles as the characteristic length, and provided a method for predicting the aerodynamic forces of bristled wings for different characteristic parameters. In order to better characterize the effect of Reynolds numbers on the aerodynamic forces of a bristled wing, Lee et al. And they also discussed the effect of Reynolds numbers on the flow field structures of the bristled wings. The virtual barriers concept was also adopted by Lee and Kim 10 to explain why the flow field structures of the bristled wings observed in flow visualization experiments are similar to those of the membrane wings. He considered this was caused by the formation of virtual barriers between the bristles on the bristle wing. 9 found that the bristled wing could produce the aerodynamic force close to that of the membrane wing, when they made rotational or translational motion at Reynolds number ( Re) about 10 ( Re is based on the mean chord-length of the wing and the mean wing-tip speed). 8.īy experimental measurements, Sunada et al. According to the existing studies on insect morphology, unlike the larger insects with membranous wings, the smallest insects have distinctive bristled wings, e.g., thrips 4, or partially bristled wings, e.g., the tiny wasp Encarsia Formosa 5, 6 the specific morphology of the bristled wings can be found in the works of Huber and Noye 5, Kolomenskiy et al. In recent years, an increasing number of researchers have focused their attention on the smallest insects, with a special focus on their flying principles and aerodynamic mechanisms. Tiny insects (with a wing length of about 0.5 mm) are abundant in nature and have significant ecological and biological importance 1, 2, 3. Therefore, the adoption of bristled wings can be beneficial during upward movement of the wings near the end of the upstroke, which may be one reason why most of the smallest insects adopt them. Thus, if the smallest insects use membrane wings, their flight muscles need to overcome large side forces in order to maintain the intended motion for less negative lift, whereas using bristled wings do not have this problem. But in the case of the flat-plate wings, although there is similar drag reduction, the side force on each wing is larger than that of the bristled wing by an order of magnitude (the underlying physical reason is discussed in the paper). In the motion of two bristled wings, the drag acting on each wing is 40% smaller than the case of a single bristled wing conducting the same motion, and only a very small side force is produced. The method of computational fluid dynamics is used in the study. Here we study the aerodynamic forces and flows of two simplified bristled wings experiencing such a motion, compared with the case of membrane wings (flat-plate wings), to see if there is any advantage in using the bristled wings. In this period, the wings may produce drag (negative vertical force) and side forces which tend to push two wings apart. It was observed that during the second half of their upstroke, the left and right wings become parallel and close to each other at the back, and move upward at zero angle of attack. Most of the smallest flying insects use bristled wings.
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