鲹科模式鱼体自主前游的标度律研究

鲹科鱼类采用波状摆动可以实现非常高效的巡游游动,在受力动态平衡下以很高的速度向前游动,其性能远超传统的人造水下航行器,因此,探寻鱼体自主前游状态下流体力和前游速度的规律并建立相应的预测式具有重要的意义.在开源OpenFOAM平台和柔性体自主推进算法基础上,实现了波动鱼体自主游动的数值模拟,以NACA0012翼型为典型鱼体外形,对鲹科模式前向自主游动开展了系统的数值模拟.由已获得的栓结模型下推力标度律的启发,分别对自主巡游下的压差力系数和摩阻力系数进行标度研究.结果表明在雷诺数从500到50 000的范围内,压差力系数和摩阻力系数分别具有形式一致的标度规律,由此可根据数值结果给出定量的预测公式,进而根据两作用力的匹配关系可以导出鱼体自主前游速度的标度律,获得了根据已知的鱼体波动参数来预估巡游速度的方法.此外,探讨了雷诺数为500和50 000工况,不同摆尾幅度和频率组合下,鱼体厚弦比对于巡游的水动力标度律和前游速度的影响,并分析了不同鱼体外形对效能比的影响,发现雷诺数越高,获得最优效能比的鱼体越细长.

STUDY ON THE SCALING LAW OF FISH-LIKE BODY SELF-PROPULSION WITH CARANGIFORM UNDULATION

During the long history of evolution, carangiform swimmers have mastered an exquisite capacity to efficiently cruise in water by undulatory locomotion. Under the dynamic balance of the fluid forces, the carangiform swimmers show excellent ability to swim forward at a high speed and its performance is far superior to traditional artificial underwater vehicles. Hence, it is of great significance to discover the scaling law of hydrodynamic forces and cruising speeds for the self-propulsion of fish, and to develop formulas for the quick estimation of the forces and forward swimming velocity. Based on the open-source OpenFOAM platform, the simulation algorithm is implemented by utilizing the flexible body self-propulsion dynamics. The forward self-propulsion motions of the NACA0012 airfoil undulating in the carangiform mode are numerically simulated. Be inspired by our earlier study on thrust scaling law for the tethered models, the pressure forces and friction forces acting on the self-propelled fish-like body are analyzed. The results indicate that the pressure force coefficients, as well as the friction drag coefficients, obey the same form of scaling law in all cases under the condition of Reynolds number between 500 and 50 000, and then the quantitative prediction formulas of the forces are obtained according to the numerical results. Furthermore, the scaling law of the forward self-propulsion velocity can be derived from the equilibrium condition between pressure force and friction force, which makes it accessible to explicitly predict the cruising speed with the undulatory motion parameters of the fish body. Also, the influence of the thickness to chord ratio of fish body on the scaling laws for the hydrodynamic forces and propulsion velocity is discussed under conditions of Re = 500 and Re = 50000, the frequency f = 0.5 ~ 2 Hz and the undulatory amplitude A = 0.05L ~ 0.1L. The effect of different fish body shapes on the energy-utilization ratio is considered, it can be found that slenderer fish body tends to achieve optimal energy-utilization ratio as the Reynolds number increases.