Turbulent-turbulent transient concept in pulsating flows
Turbulent-turbulent transient concept in pulsating flows
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DOI：
10.1017/jfm.2023.1025
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发表时间：
2024-03-07
影响因子：
3.7
通讯作者：
Seddighi，M.
中科院分区：
文献类型：
--
作者：
Taylor，P. S.;Seddighi，M.
本文研究了以水流为主导的脉动流的湍流特性。直接数值模拟已经进行了斯托克斯长度的范围内。结果表明，中低频脉动中的湍流响应是由一个多阶段的湍流-湍流过渡过程控制的，这与非周期性加速度的多阶段响应有很强的相似性。在加速初期，流动进入预转捩阶段，在壁面形成新的层流扰动边界层，流向速度条纹被拉伸。如果低速条纹不稳定之前的减速期，然后进入一个过渡阶段的扰动边界层经历一个旁路样的过渡过程。脉动流的一个独特特征是湍流衰减的持续机制，它在减速期间开始，并构成大部分周期的主要瞬态湍流机制。对于高频脉动，扰动边界层在减速期之前未能达到预转变阶段。相反，流动在两个惯性阶段之间交替，其特征在于两层放大的粘性力;一层在壁处生长，另一层分离并向核心移动。
The turbulence behaviour of current-dominated pulsating flows has been investigated. Direct numerical simulations have been carried out for Stokes lengths over a range of . The results show that the turbulence response in intermediate and low-frequency pulsations is governed by a multistage turbulent–turbulent transition process, which bears a strong similarity to the multistage response of non-periodic acceleration. During the early acceleration period, the flow enters a pretransition stage, in which a new laminar perturbation boundary layer forms at the wall, and the streamwise velocity streaks are stretched. If the low-speed streaks destabilise prior to the deceleration period, then the flow enters a transition stage in which the perturbation boundary layer undergoes a bypass-like transition process. A unique feature of pulsating flows is the ongoing mechanism of turbulence decay, which initiates during the deceleration period and constitutes the main transient turbulence mechanism for much of the cycle. For high-frequency pulsations, the perturbation boundary layer fails to reach the pretransition stage prior to the deceleration period. Instead, the flow alternates between two inertial stages which are characterised by two layers of amplified viscous force; one growing at the wall, and one detached and moving towards the core.