仿生鱼自主游动性能与机理的流固耦合研究

The outstanding performance of fish swimming have attracted the interests of bionic researches, and many kinds of bio-inspired robotic fishes have also been constructed based on biological prototypes. However, there is a gap between the robots and real fish in the swimming performance. Currently the reverse Kármán vortex street produced by bio-inspired caudal fin propulsion has been well reported, and however the key feature of the three-dimensional (3D) wake structure is not well-established for self-propelled swimming of the whole fish. Experimental investigations on live fish swimming are facing the difficulties in conducting experiments in a repeatable manner and obtaining swimming efficiency quantitatively and therefore have limitations. For solving the flow field of self-propelled swimming with complex moving deformable boundary, a fluid-structure interaction numerical method based on immersed boundary-strong coupling algorithm is proposed and corresponding solution system is developed. A numerical study on 3D multi-degree of freedom self-propelled swimming is carried out to elucidate the effect of parameters on the swimming performance and wake structure of a bio-inspired fish and further reveal the mechanism behind high-efficiency swimming. Since little attention is paid to the fluid dynamics of fish maneuvering motion, a numerical simulation which is intended to match the observation experiment on fast start is conducted. The complex 3D structure of the flow and coupling hydrodynamic characteristics under high unsteadiness during the start is analyzed to discuss the mechanism to achieve fast start. The research will provide reference for the optimal design and vorticity control of bio-inspired robotic fish and the decreasing performance gap between the robotic fish and their biological prototypes can be expected.

仿生学者已经注意到鱼类的卓越游动性能并制造了多种基于生物原型的仿生机器鱼，但所研制的样机性能与真实鱼类相比存在着不小的差距。目前仿尾鳍推进的反卡门涡街尾流已被大量报道，然而整鱼自主游动三维尾涡结构的关键特征还没有被确立起来。活鱼游动的实验研究又面临实验的可重复性、游动效率定量信息获取等困难而存在局限性。本项目针对包含复杂移动变形边界的自主游动流场的求解，提出一种基于浸入边界-强耦合算法的流固耦合数值方法并开发相应的求解系统。实施三维多自由度的自主游动数值研究，阐明各参数对仿生鱼游动性能和尾涡结构的影响，揭示高效游动的机理。针对鱼类机动运动的流体动力学问题很少得到关注的现状，进行与快速起动观测实验相匹配的数值模拟，分析起动过程中的复杂三维流动结构与高度瞬态的耦合水动力特性，探讨快速起动的实现机理。研究成果可为仿生机器鱼的优化设计与涡流控制提供参考依据，有望缩小机器鱼与生物原型之间的性能差距。

仿生学者已经注意到鱼类的卓越游动性能并制造了多种基于生物原型的仿生机器鱼，但所研制的样机性能与真实鱼类相比存在着不小的差距。目前仿尾鳍推进的反卡门涡街尾流已被大量报道，然而整鱼自主游动三维尾涡结构的关键特征还没有被确立起来。活鱼游动的实验研究又面临实验的可重复性、游动效率定量信息获取等困难而存在局限性。. 针对包含复杂移动变形边界的自主游动流场的求解，研究快速、健壮的流-固交界面信息传递方法，突破稳定、精确的流-固强耦合数值求解技术，提出一种基于浸入边界-强耦合算法的流固耦合数值方法并开发相应的求解系统。就所提出的数值方法应用于若干标准算例及所关注的自主游动问题的模拟，与已出版的实验和计算结果进行比较，验证了流固耦合求解系统的精确性和可靠性。. 对仿生黄貂鱼的三维多自由度自主游动进行了模拟和分析，结果表明：黄貂鱼的形态学和运动学特性允许它在慢速和快速游动情况下均有较高的效率；在黄貂鱼鼻部附近的马蹄形涡，以及分别位于胸鳍前缘上部和下部的前缘涡对推力产生起关键作用；分别位于胸鳍波动变形时上表面的波谷中和下表面的波峰上的两个特殊涡结构在水和鱼体之间起到润滑的作用，使表面剪应力减小。尽管波动胸鳍为复杂升力面，仍可建立自主巡游速度与波动频率之间的线性关系；随着胸鳍波动频率的增加，各主要涡结构的定性特征未发生改变，但定量上它们的尺寸和强度变得更大。. 对仿生金枪鱼的C型起动进行了模拟和分析，结果表明：在起动阶段1，鱼体后部快速地弯曲成C型，摇艏角速度快速向负向（顺时针方向）增加至峰值之后缓慢减小，鱼体快速转向；在起动阶段2，鱼体后部快速地解除弯曲并伴随尾鳍摆动，摇艏角速度快速向正向（逆时针方向）增加至峰值之后迅速减小，纵向速度快速向前进方向增加至幅值之后保持不变。在C型起动中共有两个涡环形成，每个涡环产生一个射流，在阶段1所产生的射流使鱼体快速转向，在阶段2所产生的射流使鱼体快速向前游动。