鳍条运动模式对仿生波动鳍推进力影响的研究

仿生波动鳍的鳍条运动模式分为等幅和变幅两种类型,通过实验发现这2种鳍条运动模式下所产生的游动性能存在着较大的差异.为了揭示这种差异存在的内在缘由,建立基于鳍条这2种运动模式的仿生波动鳍运动学方程.利用计算流体动力学原理,比较不同运动学参数下2种运动模式鳍面压力分布情况,分别给出2种模式下波动鳍产生的无量纲阻力系数随时间的变化情况以及无量纲阻力系数时间平均值随频率、摆幅和波长的变化规律,给出鱼鳍模型中部沿鳍条方向切面的速度场和压力场.结果表明:2种模式下产生的推进力均随频率、摆幅和波长的增大而增加,但等幅摆动产生的推进力始终小于变幅摆动;2种模式下模型中部切面的速度场和压力场存在明显的差异,而尾迹二维涡量场结构和分布形态十分相似,说明影响2种模式游动效果的主要原因之一来自于沿鳍条方向的差异.结论进一步阐述了依赖鱼鳍波动推进的水生生物体高效游动的本质,也为研制高性能的仿鱼鳍波动推进装置提供了参考.

Research on influence of fin ray motion pattern on the propulsion of bionic undulating fins

The motion patterns of fin ray of a bionic undulating fin are normally divided into two types:constant amplitude and variable amplitude.The initial experimental tests reveal that there are significant differences on propulsion performences between these two motion patterns.In or-der to reveal the inherent cause for such differences,a bionic undulating fin was developed and the relevant kinematic equations were established.By taking the advantages of computational fluid dynamic (CFD),the pressure distribution on fin surface under different kinematic parame-ters was compared.The variation of non-dimensional drag coefficient with time under the two patterns was presented.Meanwhile,the variation of time-averaged non-dimensional drag coeffi-cient with undulating frequency,amplitude and wavelength was also presented.In addition,the velocity contour and pressure contour in transversal surface along fin ray were illustrated.The results showed that:the time-averaged propulsion force increased with the increasement of fre-quency,amplitude and wavelength.However,the force produced by constant amplitude was al-ways less than that of variable amplitude.Moreover,the velocity contour and pressure contour in transversal surface along fin ray between the two motion patterns were of great differences,but little differences were occurred in the vortex distribution in the longitudinal cross-section along fin,which indicated that the main influence of the two motion patterns might be from the trans-versal section along fin ray.A further discussion is implemented to illustrate the principle of a-quatic organisms with undulating fins that propel themselves effectively.It provides a reference for the development of a high performance bionic undulating fin propulsion system.