Bifurcations to turbulence in transitional channel flow
Bifurcations to turbulence in transitional channel flow
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DOI：
10.1103/physrevfluids.4.113903
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发表时间：
2019-11-22
影响因子：
2.7
通讯作者：
Manneville, Paul
中科院分区：
文献类型：
--
作者：
Shimizu, Masaki;Manneville, Paul
在有壁面边界的平行流中，即使层流仍然稳定，也会出现持续的湍流。槽道流是这样的流动之一，并显示局部湍流的时空波动模式沿着其路径从和到无特征的湍流。通过直接数值模拟，我们研究了观察到的不一致性湍流衰减根据二维定向渗流（2D-DP）方案和持续的倾斜本地化湍流带（LTB）的DP临界点以下的存在。在雷诺数Re-g约为700以上，观察到持续的LTB;大多数LTB具有相同的取向，因此，在Re-2约为1000以下，LTB模式的展向对称性被破坏。横向分裂的频率在Re-g < Re < Re-2的范围内增加，通过横向分裂，LTB产生另一个具有相反方向的分裂，使得湍流传播本质上变成二维的。它在Re-2时达到临界速率，超过该临界速率，对称性恢复。仅在Re-2以上检索2D-DP行为。提出了一个平均场模型，该模型通过考虑沿任一方向传播的LTB的空间平均密度之间的相互作用，定性地解释了上述混沌恢复分叉。
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 (2D-DP) scenario and the presence of sustained oblique localized turbulent bands (LTBs) below the DP critical point. Above Reynolds number Re-g approximate to 700, sustained LTBs are observed; most LTBs have the same orientation so that the spanwise symmetry of the LTB pattern is broken below Re-2 approximate to 1000. 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 Re-g < Re < Re-2. It reaches a critical rate at Re-2, beyond which symmetry is restored. The 2D-DP behavior is retrieved only above Re-2. 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.