Zhang Chao, Hedrick Tyson L, Mittal Rajat
Department of Mechanical Engineering, the Johns Hopkins University, Baltimore, Maryland, United States of America.
Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America.
PLoS One. 2015 Aug 7;10(8):e0132093. doi: 10.1371/journal.pone.0132093. eCollection 2015.
Despite intense study by physicists and biologists, we do not fully understand the unsteady aerodynamics that relate insect wing morphology and kinematics to lift generation. Here, we formulate a force partitioning method (FPM) and implement it within a computational fluid dynamic model to provide an unambiguous and physically insightful division of aerodynamic force into components associated with wing kinematics, vorticity, and viscosity. Application of the FPM to hawkmoth and fruit fly flight shows that the leading-edge vortex is the dominant mechanism for lift generation for both these insects and contributes between 72-85% of the net lift. However, there is another, previously unidentified mechanism, the centripetal acceleration reaction, which generates up to 17% of the net lift. The centripetal acceleration reaction is similar to the classical inviscid added-mass in that it depends only on the kinematics (i.e. accelerations) of the body, but is different in that it requires the satisfaction of the no-slip condition, and a combination of tangential motion and rotation of the wing surface. Furthermore, the classical added-mass force is identically zero for cyclic motion but this is not true of the centripetal acceleration reaction. Furthermore, unlike the lift due to vorticity, centripetal acceleration reaction lift is insensitive to Reynolds number and to environmental flow perturbations, making it an important contributor to insect flight stability and miniaturization. This force mechanism also has broad implications for flow-induced deformation and vibration, underwater locomotion and flows involving bubbles and droplets.
尽管物理学家和生物学家进行了深入研究，但我们仍未完全理解将昆虫翅膀形态和运动学与升力产生联系起来的非定常空气动力学。在此，我们制定了一种力分配方法（FPM），并在计算流体动力学模型中实施，以将空气动力明确且直观地划分为与翅膀运动学、涡度和粘性相关的分量。将FPM应用于天蛾和果蝇飞行表明，前缘涡是这两种昆虫产生升力的主要机制，占净升力的72 - 85%。然而，还存在另一种此前未被识别的机制，即向心加速度反应，它产生的净升力高达17%。向心加速度反应类似于经典的无粘附加质量，因为它仅取决于物体的运动学（即加速度），但不同之处在于它需要满足无滑移条件，以及翅膀表面的切向运动和旋转的组合。此外，经典的附加质量力对于循环运动恒为零，但向心加速度反应并非如此。此外，与涡度产生的升力不同，向心加速度反应升力对雷诺数和环境流动扰动不敏感，这使其成为昆虫飞行稳定性和小型化的重要贡献因素。这种力机制对流动诱导的变形和振动、水下运动以及涉及气泡和液滴的流动也具有广泛影响。
