The transition to turbulence in Taylor-Couette flow often occurs via a sequence of supercritical bifurcations to progressively more complex, yet stable, flows. We describe a subcritical laminar-turbulent transition in the counter-rotating regime mediated by an unstable intermediate state in a system with an axial aspect ratio of $\Gamma=5.26$ and a radius ratio of $\eta=0.905$. In this regime, flow visualization experiments and numerical simulations indicate the intermediate state corresponds to an aperiodic flow featuring interpenetrating spirals. Furthermore, the reverse transition out of turbulence leads first to the same intermediate state, which is now stable, before returning to an azimuthally-symmetric laminar flow. Time-resolved tomographic particle image velocimetry is used to characterize the experimental flows; these measurements compare favorably to direct numerical simulations with axial boundary conditions matching those of the experiments.

中文翻译：

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具有反向旋转圆柱体的 Taylor-Couette 流中向湍流的新型亚临界转变

Taylor-Couette 流向湍流的转变通常是通过一系列超临界分岔到逐渐复杂但稳定的流动发生的。我们描述了在轴向纵横比为 $\Gamma=5.26$ 和半径比为 $\eta=0.905$ 的系统中由不稳定中间状态介导的反向旋转状态中的亚临界层流-湍流转变。在这种情况下，流动可视化实验和数值模拟表明中间状态对应于具有互穿螺旋的非周期性流动。此外，湍流的反向过渡首先导致相同的中间状态，现在稳定，然后返回到方位角对称的层流。时间分辨断层扫描粒子图像测速仪用于表征实验流程；