The Gymnarchus niloticus fish can swim in surging and heaving directions only with a long undulating ribbon fin while keeping its body along almost straight line. These features substantially inspire the design of underwater vessels with high maneuverability and station keeping performance, which is characterized by peculiar vortex structures induced by undulating fin propulsion. To reveal the propulsion mechanism under the evolution of these complex vortex structures, the variation of velocity field with the undulating fin’s wave phase on cross section and mid-sagittal plane at wave amplitude of 85° is investigated by phase-locked digital particle image velocimetry (DPIV). Through experimental flow field images, two typical vortex structures are clearly identified, i.e., streamwise vortex and crescent vortex, which is further explained by supplemental numerical simulations using large eddy simulation. Vortex characteristic and its evolution on cross sections and mid-sagittal planes is investigated, and its relationship with thrust, heave force is also analyzed. It is found that the two kinds of vortexes induce the main hydrodynamic forces in two directions synchronously, which brings the undulating fin propulsion an extra-ordinal maneuverability. The research will be useful for understanding the potential mechanism of this novel propulsion and is of great application prospect in designing more maneuverable underwater vehicles.

该裸臀鱼科罗非鱼鱼只能用长长的波浪状带状鳍，同时保持身体几乎呈直线状，才能向汹涌起伏的方向游动。这些特点极大地激发了具有高机动性和站位保持性能的水下船舶的设计，其特点是由波浪形鳍推进引起的特殊涡流结构。为揭示这些复杂涡结构演化下的推进机制，利用锁相数字粒子图像测速仪研究了波幅为85°时波浪形鳍在横截面和中矢状面上波相位随波幅波相位的变化。 DPIV）。通过实验流场图像，可以清楚地识别出两种典型的涡结构，即流向涡和新月涡，使用大涡模拟的补充数值模拟进一步解释了这一点。研究了涡流特征及其在横截面和中矢状面上的演化，并分析了其与推力、垂荡力的关系。研究发现，两种涡流在两个方向上同步产生主要的水动力，使波浪形鳍片推进具有非凡的机动性。该研究将有助于了解这种新型推进器的潜在机制，在设计更具机动性的水下航行器方面具有广阔的应用前景。研究发现，两种涡流在两个方向上同步产生主要的水动力，使波浪形鳍片推进具有非凡的机动性。该研究将有助于了解这种新型推进器的潜在机制，在设计更具机动性的水下航行器方面具有广阔的应用前景。研究发现，两种涡流在两个方向上同步产生主要的水动力，使波浪形鳍片推进具有非凡的机动性。该研究将有助于了解这种新型推进器的潜在机制，在设计更具机动性的水下航行器方面具有广阔的应用前景。