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A computational investigation of lift generation and power expenditure of Pratt’s roundleaf bat (Hipposideros pratti) in forward flight

机译：普拉特圆叶蝙蝠（Hipposideros pratti）向前飞行时升力产生和功率消耗的计算研究

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The aerodynamic mechanisms of bat flight have been studied using a numerical approach. Kinematic data acquired using a high resolution motion capture system was employed to simulate the unsteady air flow around a bat’s wings. A flapping bat wing contains many degrees of freedom, which make 3D motion tracking challenging. In order to overcome this challenge, an optical motion capture system of 21 cameras was used to reduce wing self-occlusion. Over the course of a meter-long flight, 108 discrete marker points on the bat’s wings (Pratt’s roundleaf bat, Hipposideros pratti) were tracked. The time evolution of the surface of each wing was computationally reconstructed in 3D space. The resulting kinematic model was interfaced with an unsteady incompressible flow solver using the immersed boundary method (IBM) and large eddy simulation (LES). Verification and validation of the flow simulation were conducted to establish accuracy. The aerodynamic forces calculated from the simulation compared well to the forces theoretically needed to sustain the observed flight trajectory. The transient flow field generated by the simulation allowed for the direct calculation of lift, drag, and power output of the bat during flight. The mean lift coefficient was found to be 3.21, and the flap cycle averaged aerodynamic power output was 1.05 W. Throughout the flap cycle, the planform area of the wings varied up to 46% between the largest and smallest values. During the upstroke, wing rotation was found to mitigate negative lift thereby improving overall flight efficiency. The high resolution motion capture and flow simulation framework presented here has the potential to facilitate the understanding of complex bat flight aerodynamics for both straight and maneuvering flight modes.
机译：使用数值方法研究了蝙蝠飞行的空气动力学机理。使用高分辨率运动捕捉系统获取的运动学数据用于模拟蝙蝠翅膀周围的不稳定气流。拍打的蝙蝠翼包含许多自由度，这使3D运动跟踪具有挑战性。为了克服这一挑战，使用了21台摄像机的光学运动捕捉系统来减少机翼的自闭塞。在长达一米的飞行过程中，跟踪了蝙蝠翅膀上108个离散的标记点（普拉特的圆叶蝙蝠，希波塞德罗斯·普拉蒂）。在3D空间中通过计算重建了每个机翼表面的时间演化。使用沉浸边界方法（IBM）和大涡模拟（LES），将生成的运动学模型与非定常不可压缩流求解器接口。进行流动模拟的验证和确认以建立准确性。通过仿真计算得出的空气动力与理论上维持观测的飞行轨迹所需的力进行了很好的比较。通过模拟生成的瞬态流场可以直接计算飞行过程中蝙蝠的升力，阻力和功率输出。发现平均升力系数为3.21，襟翼循环的平均空气动力输出为1.05W。在整个襟翼循环中，机翼的平面面积在最大值和最小值之间变化高达46％。在上冲程期间，发现机翼旋转减轻了负升力，从而提高了总体飞行效率。此处介绍的高分辨率运动捕获和流动模拟框架具有促进理解直线飞行和机动飞行两种复杂蝙蝠飞行空气动力学的潜力。

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