School of Engineering , Grand Valley State University, Grand Rapids, MI 49504, USA.
Department of Mechanical Engineering, Virginia Tech, Blacksburg, VA 24060, USA.
J Exp Biol. 2021 Jul 15;224(14). doi: 10.1242/jeb.233635. Epub 2021 Jul 23.
Flying snakes flatten their body to form a roughly triangular cross-sectional shape, enabling lift production and horizontal acceleration. While gliding, they also assume an S-shaped posture, which could promote aerodynamic interactions between the fore and the aft body. Such interactions have been studied experimentally; however, very coarse models of the snake's cross-sectional shape were used, and the effects were measured only for the downstream model. In this study, the aerodynamic interactions resulting from the snake's posture were approximated using two-dimensional anatomically accurate airfoils positioned in tandem to mimic the snake's geometry during flight. Load cells were used to measure the lift and drag forces, and flow field data were obtained using digital particle image velocimetry (DPIV). The results showed a strong dependence of the aerodynamic performance on the tandem arrangement, with the lift coefficients being generally more influenced than the drag coefficients. Flow field data revealed that the tandem arrangement modified the separated flow and the wake size, and enhanced the lift in cases in which the wake vortices formed closer to the models, producing suction on the dorsal surface. The downforce created by the flow separation from the ventral surface of the models at 0 deg angle of attack was another significant factor contributing to lift production. A number of cases showing large variations of aerodynamic performance included configurations close to the most probable posture of airborne flying snakes, suggesting that small postural variations could be used to control the glide trajectory.
飞蛇会将身体压扁成大致的三角形横截面形状，从而产生升力并实现水平加速。在滑翔过程中，它们还会呈现出 S 形姿势，这有助于促进蛇体前后部分之间的空气动力学相互作用。这些相互作用已经通过实验进行了研究；然而，所使用的蛇类横截面形状模型非常粗糙，并且仅测量了下游模型的效果。在这项研究中，通过将两个二维解剖学上精确的翼型排列成串联的方式来模拟蛇类在飞行过程中的几何形状，从而近似地模拟出蛇类姿势产生的空气动力学相互作用。使用测力传感器来测量升力和阻力，使用数字粒子图像测速（DPIV）获得流场数据。结果表明，空气动力学性能强烈依赖于串联布置，升力系数通常比阻力系数更受影响。流场数据表明，串联布置改变了分离流和尾流的大小，并在尾流涡旋更靠近模型形成、在背部产生吸力的情况下增强了升力。模型腹侧表面的流动分离产生的向下力是产生升力的另一个重要因素。一些表现出显著的空气动力学性能变化的案例包括与最有可能的飞行中飞蛇姿势接近的配置，这表明微小的姿势变化可以用于控制滑翔轨迹。
