输入扰动对波动鳍推进性能影响的研究

Research on the effect of input perturbation on the propulsion performance of an undulating fin

输入扰动对波动鳍推进性能影响是一个新兴的研究领域。本文分析了高频率、小幅度和短波长的正弦波形叠加于波动鳍上时对波动鳍推进力的影响。建立运动学模型,利用四面体网格对计算区域进行划分,采用非耦合隐式求解器求解非定常不可压缩N-S方程和连续性方程。给出计算条件,并对算法给予验证。比较等波幅和变波幅两种正弦扰动波形下,波动鳍的无量纲阻力系数、阻力系数均值以及涡量场随周期(0.05 s、0.1 s、0.3 s、0.5 s、0.8 s)、幅度(0.0008 m、0.001 m、0.0015 m)和波长(0.002 m、0.008 m、0.012 m)的变化情况,从涡动力学角度对该影响进行解释。结果显示:输入扰动不仅影响了波动鳍前缘涡的传递,并对波动鳍周边及尾迹区域漩涡数量和强度产生了改变。除在特定条件外,输入扰动对波动鳍推进力产生负面影响,变波幅扰动的影响要大于等波幅情况。该研究可为波动鳍选择合适参数的输入扰动以提高推进力提供参考。

The effect of input perturbation on the propulsion performance of an undulating fin is one of the new research fields.In this paper,we considered the effects of adding high-frequency,low-amplitude,shortwavelength perturbations to a smooth sinusoidal base input signal for an undulating fin on its propulsion force generation.A kinematic model was established,the calculation area was partitioned using tetrahedral grid,the unsteady incompressible N-S equation and continuity equation were solved by an uncoupled implicit solver.The computational conditions were presented and the algorithm was subsequently verified.The change of non-dimensional drag coefficient,the mean drag coefficient and vorticity field of undulating fin with input perturbation periods(0.05 s,0.1 s,0.3 s,0.5 s,0.8 s),amplitudes(0.0008 m,0.001 m,0.0015 m)and wavelengths(0.002 m,0.008 m,0.012 m)under two amplitude modes(constant amplitude and variable amplitude)of input perturbation were investigated.The phenomena were explained from the perspective of vortex dynamics.The results demonstrate that the input perturbation not only affects the propagation of leading edge vortex,but also affects the vorticity structure by altering the magnitude and numbers in the wake or around the undulating fin.Generally speaking,the input perturbation has a negative impact on undulating fin propulsion force except for some specified conditions.Besides,the variable amplitude mode of input perturbation has more significant effect on propulsion force than the constant amplitude mode.The current study provides references for researchers to choose appropriate parameters of input perturbation to improve the propulsion force of undulating fin.