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The uniform-momentum zones and internal shear layers in turbulent pipe flows at Reynolds numbers up to Reτ=1000
International Journal of Heat and Fluid Flow ( IF 2.6 ) Pub Date : 2021-05-07 , DOI: 10.1016/j.ijheatfluidflow.2021.108817
Xue Chen , Yongmann M. Chung , Minping Wan

The statistical characteristics of the internal shear layers (ISL) and the coherent structures around the ISLs in turbulent pipe flows are examined using direct numerical simulation data at four Reynolds numbers Reτ=180, 360, 500 and 1000. The ISLs are defined by the peaks on the velocity gradients with no ad hoc filter applied on the ISL selection. This is different from the previous studies where uniform momentum zones (UMZs) are identified first using a velocity histogram and then the ISL is defined as an UMZ interface. In this study, ISLs are ranked by both their strength and location. The signature behaviours of the ISL including an abrupt streamwise velocity jump and a sharp decrease in velocity fluctuation across the ISL are confirmed. Both the positive and the negative ISLs are stronger towards the wall. The local imbalance between ejections and sweeps are observed around ISLs. Near-wall ISLs have stronger ejections while ISLs in the pipe centre have stronger sweeps. The balance between ejection and sweep is achieved approximately at 0.55-0.6 of the pipe radius for the range of Reynolds numbers studied. The flow structures around an ISL have been identified via 3D conditional sampling. The average positive ISL is located between the high-speed streak above and the low-speed streak below. The low-speed streak is associated with a pair of counter-rotating streamwise vortices which result in a strong ejection around the ISL.



中文翻译:

湍流管中的均匀动量带和内部剪切层的雷诺数最大为 关于τ=1000

使用四个雷诺数下的直接数值模拟数据检查了湍流中内部剪切层(ISL)和ISL周围相干结构的统计特性 关于τ=180,360、500和1000。ISL是由速度梯度上的峰值定义的,没有在ISL选择上应用ad hoc过滤器。这与先前的研究不同,在先前的研究中,首先使用速度直方图确定了统一的动量区域(UMZ),然后将ISL定义为UMZ接口。在这项研究中,ISL的强度和位置都对其进行排名。确认了ISL的签名行为,包括突然的沿流速度跳跃和跨ISL的速度波动急剧下降。积极的和消极的ISL都朝着隔离墙方向发展。在ISL周围观察到喷射和扫掠之间的局部不平衡。近壁ISL具有更强的弹射性,而管道中心的ISL具有更强的扫掠性。喷射和扫掠之间的平衡大约在0.55--0.6雷诺数范围内的管道半径的变化。已通过3D条件采样识别了ISL周围的流动结构。平均正ISL位于上方的高速条纹和下方的低速条纹之间。低速条纹与一对反向旋转的涡流相关,导致ISL周围强烈喷出。

更新日期:2021-05-08
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