Matta Alexander, Bayandor Javid, Battaglia Francine, Pendar Hodjat
CRashworthiness for Aerospace Structures and Hybrids (CRASH) Lab, Department of Mechanical and Aerospace Engineering, University at Buffalo, The State University of New York, Buffalo, NY 14260, USA
CRashworthiness for Aerospace Structures and Hybrids (CRASH) Lab, Department of Mechanical and Aerospace Engineering, University at Buffalo, The State University of New York, Buffalo, NY 14260, USA.
Biol Open. 2019 Jul 18;8(7):bio040626. doi: 10.1242/bio.040626.
Scombrid fish lunate caudal fins are characterized by a wide range of sweep angles. Scombrid that have small sweep-angle caudal fins move at higher swimming speeds, suggesting that smaller angles produce more thrust. Furthermore, scombrids occasionally use high angles of attack (AoA) suggesting this also has some thrust benefit. This work examined the hypothesis that a smaller sweep angle and higher AoA improved thrust in swimmers by experimentally analyzing a robophysical model. The robophysical model was tested in a water tunnel at speeds between 0.35 and 0.7 body lengths per second. Three swept caudal fins were analyzed at three different AoA, three different freestream velocities, and four different Strouhal numbers, for a total of 108 cases. Results demonstrated that the fin with the largest sweep angle of 50° resulted in lower thrust production than the 40° and 30° fins, especially at higher Strouhal numbers. Larger AoA up to 25° increased thrust production at the higher Strouhal numbers, but at lower Strouhal numbers, produced less thrust. Differences in thrust production due to fin sweep angle and AoA were attributed to the variation in spanwise flow and leading edge vortex dynamics.
鲭科鱼类的新月形尾鳍具有多种后掠角。后掠角较小的鲭科鱼类游动速度更快，这表明较小的后掠角能产生更大的推力。此外，鲭科鱼类偶尔会采用大攻角，这表明大攻角也能带来一定的推力优势。本研究通过对一个机器人物理模型进行实验分析，验证了较小的后掠角和较大的攻角能提高游泳者推力的假设。该机器人物理模型在水洞中以每秒0.35至0.7倍体长的速度进行测试。对三种后掠尾鳍在三种不同攻角、三种不同自由流速度和四种不同斯特劳哈尔数下进行了分析，共计108种情况。结果表明，后掠角最大为50°的尾鳍产生的推力低于40°和30°的尾鳍，尤其是在较高的斯特劳哈尔数下。在较高的斯特劳哈尔数下，高达25°的较大攻角会增加推力产生，但在较低的斯特劳哈尔数下，产生的推力较小。尾鳍后掠角和攻角导致的推力产生差异归因于展向流和前缘涡动力学的变化。
