Mukund Vasudevan, Paranjape Chaitanya S, Sitte Michael Philip, Yalnız Gökhan, Hof Björn
Institute of Science and Technology Austria (ISTA), Klosterneuburg, Austria.
Nat Commun. 2025 Sep 26;16(1):8447. doi: 10.1038/s41467-025-63044-7.
The recent classification of the onset of turbulence as a directed percolation (DP) phase transition has been applied to all major shear flows including pipe, channel, Couette and boundary layer flows. A cornerstone of the DP analogy is the memoryless (Poisson) property of turbulent sites. We here show that, for the classic case of channel flow, neither the decay nor the proliferation of turbulent stripes is memoryless. As demonstrated by a standard analysis of the respective survival curves, isolated channel stripes, in the immediate vicinity of the critical point, age. Consequently, the one to one mapping between turbulent stripes and active DP-sites is not fulfilled in this low Reynolds number regime. In addition, the interpretation of turbulence as a chaotic saddle with supertransient properties, the basis of recent theoretical progress, does not apply to individual localized stripes. The discrepancy between channel flow and the transition models established for pipe and Couette flow, illustrates that seemingly minor geometrical differences between flows can give rise to instabilities and growth mechanisms that fundamentally alter the nature of the transition to turbulence.
最近将湍流起始归类为有向渗流（DP）相变的方法已应用于所有主要的剪切流，包括管道流、槽道流、库埃特流和边界层流。DP类比的一个基石是湍流区域的无记忆（泊松）特性。我们在此表明，对于槽道流的经典情况，湍流条纹的衰减和增殖都不是无记忆的。正如对各自生存曲线的标准分析所表明的那样，在临界点附近孤立的槽道条纹会老化。因此，在这个低雷诺数区域，湍流条纹与活跃DP位点之间的一一映射并不成立。此外，将湍流解释为具有超瞬态特性的混沌鞍点，这是近期理论进展的基础，但并不适用于单个局部条纹。槽道流与为管道流和库埃特流建立的过渡模型之间的差异表明，流之间看似微小的几何差异可能会引发不稳定性和增长机制，从而从根本上改变向湍流过渡的性质。
