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Bifurcations to turbulence in transitional channel flow
Physical Review Fluids ( IF 2.5 ) Pub Date : 2019-11-22 , DOI: 10.1103/physrevfluids.4.113903
Masaki Shimizu , Paul Manneville

In wall-bounded parallel flows, sustained turbulence can occur even while laminar flow is still stable. Channel flow is one of such flows and displays spatiotemporal fluctuating patterns of localized turbulence along its way from and to featureless turbulence. By direct numerical simulation, we study the observed inconsistency between turbulence decay according to a two-dimensional directed-percolation (2DDP) scenario and the presence of sustained oblique localized turbulent bands (LTBs) below the DP critical point. Above Reynolds number Reg700, sustained LTBs are observed; most LTBs have the same orientation so that the spanwise symmetry of the LTB pattern is broken below Re21000. The frequency of transversal splitting, by which an LTB generates another one with opposite obliqueness, so that turbulence spreading becomes intrinsically two dimensional, increases in the range Reg<Re<Re2. It reaches a critical rate at Re2, beyond which symmetry is restored. The 2DDP behavior is retrieved only above Re2. A mean-field model is proposed which qualitatively accounts for the above symmetry-restoring bifurcation by considering interactions between space-averaged densities of LTBs propagating in either direction.

中文翻译:

过渡通道中湍流的分叉

在有边界的平行流中,即使层流仍然稳定,也会发生持续的湍流。通道流就是这样的流之一,它显示了从湍流到无特征湍流的局部湍流的时空波动模式。通过直接数值模拟,我们研究了根据二维定向渗流观察到的湍流衰减之间的不一致2个d-DPDP临界点以下的情况以及持续倾斜的局部湍流带(LTB)的存在。雷诺数以上回覆G700,观察到持续的LTBs;大多数LTB具有相同的方向,因此LTB模式的翼展方向对称性在下面被破坏回覆2个1000。横向分裂的频率在范围内增加,横向分裂的频率增加,LTB通过该频率生成另一个具有相反斜度的分裂,从而湍流扩展本质上是二维的回覆G<回覆<回覆2个。达到临界速度回覆2个,超出此范围即可恢复对称性。这2个d-DP 行为仅在上方检索 回覆2个。提出了一种平均场模型,该模型通过考虑在任一方向上传播的LTB的空间平均密度之间的相互作用来定性地解释上述对称恢复分叉。
更新日期:2019-11-22
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