Supporting data for "Hydrodynamic Instabilities of Active Jets"

Abstract of manuscript:Using a combination of theory, experiments, and numerical simulations, we investigate the stability of coherent structures in a suspension of strongly aligned active swimmers. We show that a dilute jet of pullers undergoes a pearling instability, while a jet of pushers exhibits a helical (or, in two dimensions, zigzag) instability. We further characterise the nonlinear evolution of these instabilities, deriving exact and approximate solutions for the spreading and mutual attraction of puller clusters, as well as the wavelength coarsening of the helical instability. Our theoretical predictions closely match the experimentally observed wavelengths, timescales, and flow fields in suspensions of photophobic algae, as well as results from direct numerical simulations. These findings reveal the intrinsic instability mechanisms of aligned active suspensions and demonstrate that coherent structures can be destabilised by the flows they generate.

论文摘要：本研究结合理论分析、实验观测与数值模拟方法，探究强对齐活性游泳者（active swimmers）悬浮体系内相干结构（coherent structures）的稳定性。研究发现，稀疏拉式游泳者（pullers）射流会发生串珠失稳（pearling instability），而推式游泳者（pushers）射流则呈现螺旋失稳（helical instability，二维情形下表现为锯齿形zigzag失稳）。本研究进一步对两类失稳的非线性演化过程开展表征工作，推导得到拉式游泳者集群的扩散与相互吸引的精确解与近似解，以及螺旋失稳的波长粗化规律。理论预测结果与趋避光藻类（photophobic algae）悬浮液中实验观测得到的波长、时间尺度与流场特征，以及直接数值模拟（direct numerical simulations）结果均高度吻合。上述研究揭示了对齐活性悬浮体系的内在失稳机制，并证实相干结构可由其自身产生的流场触发失稳。