Aerodynamics of flapping wings in forward flight

飞行的昆虫既能长时间悬停，又能拍打翅膀进行高度机动。人们对扑翼及其飞行力学进行了大量的研究，极大地促进了仿生无人机的发展。尽管如此，仍然很难说到目前为止完成的技术足以描述扑翼系统的整体情况。因此，仿生无人机的发展还没有跃升到一定的水平。在扑翼空气动力学的最新趋势中，一个值得注意的问题是，大多数研究仍然强烈地将自己的范围限制在悬停飞行上，尽管对于大多数飞行昆虫来说，停留在太空中的特定点是非常罕见的(它们通常以特定的首选能量最佳飞行速度飞行)。对杠杆的研究也在很大程度上依赖于悬停状态，即身体停留在固定点，翅膀在没有自由流的情况下沿水平冲程平面移动。在这些研究中，提前率一直被认为是零，它也是控制LEV行为的一个主要因素。昆虫前向飞行时的两个明显的运动学特征，即倾斜和后移的冲程平面，可以显著改变跨向流动从而影响杠杆，目前也没有得到充分的研究。很少有研究试图揭示前进比的影响，几乎没有报道过肤浅的东西，因为它们依赖于简化的运动轮廓和与悬停状态相比略微延长的条件。由于缺乏对前飞的了解，空气动力学模型的发展长期停滞不前。所有关于飞行动力学的研究都只能涵盖近悬停动作，本课题旨在对前飞扑翼的空气动力学问题进行深入的研究。详细研究了固定自由流中不同运动学和流体构型的小展弦比平板的气动特性，建立了一种新的气动模型，该模型可以包含冲程平面的前进率、展弦比、后掠角和倾角的气动特性，从而可以扩展到各种飞行模式。利用空气动力学模型和实例昆虫的形态数据对飞行稳定性进行了分析。这将使我们对前飞的稳定性和可控性有更好的了解。

Flying insects are capable of both long-term hovering and high-degree of maneuvering with flapping wings. There have been a lot of studies on the flapping wings and their flight mechanics, bringing on a great improvement in the development of biomimetic drones. Nonetheless, it is still hard to say that the techniques accomplished so far are sufficient to describe the flapping-wing systems overall. Accordingly, the biomimetic drone development also has not jumped over a certain level. One notable issue in the recent trends in flapping-wing aerodynamics is that most studies still strongly confine own scopes to the hovering flight, despite the fact that staying particular point in space is very rare for most flying insects (they usually fly with a certain preferred – energy optimum – flight speed). The studies on the LEV also have heavily relied on the hovering state where a body stays at a fixed point and the wings move along the horizontal stroke plane without freestream. The advance ratio, which is also one primary element governing the LEV behavior, has been regarded as zero in these studies. Two distinctive kinematic features of flying insects in forward flight, i.e., the inclined and shifted-back stroke plane, which can significantly change the spanwise flow thereby impacting the LEV, have not yet been sufficiently investigated either. Few studies trying to reveal the effect of advance ratio had barely managed to report superficial things, because they relied on simplified motion profiles and marginally extended conditions from that in hover. A lack of such knowledge about forward flight brings on long-term stagnancy in aerodynamic model development. All the studies on flight dynamics are only able to cover near-hover maneuvers.With this program, this applicant proposes a thorough investigation on the aerodynamics of flapping wings in forward flight. The LEV characteristics on low-aspect-ratio flat plates at various kinematic and fluidic configurations in a fixed freestream will be explored in detail, and a novel aerodynamic model, which can encompass the LEV characteristics with respect to the advance ratio, aspect ratio, sweptback angle, and the angle of inclination of the stroke plane thereby being expandable to various flight modes, will be established. The flight stability analysis by using the aerodynamic model and morphological data of an example insect will also follow. This will give us better insights on the stability and controllability in forward flight.