Taylor hypothesis and large-scale coherent structures
Taylor hypothesis and large-scale coherent structures
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DOI：
10.1017/s0022112081000463
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发表时间：
1981-11
影响因子：
3.7
通讯作者：
K. Zaman;A. Hussain
中科院分区：
文献类型：
--
作者：
K. Zaman;A. Hussain
本文通过比较剪切湍流中大尺度相干结构的实际空间分布与泰勒假设的适用性，对大尺度相干结构的适用性进行了评价。这项研究已在近场的7[sdot ]62厘米的圆形空气射流在射流雷诺数为3[sdot ]2 × 104，其中的相干结构和它们的相互作用已组织通过控制激发。通过相位平均热线数据获得了结构特性的实际分布，在固定相位的结构横截面范围内的不同空间点重复测量。相应的“空间”分布的这些属性（通过使用泰勒假设）从时间数据在适当的阶段和位置，表明该假设工作得很好，为一个孤立的相干结构，如果一个恒定的对流速度，等于结构中心的速度，在假设中使用的剪切流无处不在。当地时间平均甚至瞬时流向速度的普遍使用产生不可接受的大失真。当结构相互作用，如配对参与，没有对流速度可以找到的假设工作。定量地确定了Navier-Stokes方程中对相平均涡度有贡献但被假设忽略的项的分布。这表明，与背景湍流场有关的项可以忽略，而与相干运动场有关的项则不能忽略。特别是，由于相干运动场的压力项是大的，不能忽略。
The applicability of the Taylor hypothesis to large-scale coherent structures in turbulent shear flows has been evaluated by comparing the actual spatial distributions of the structure properties with those deduced through the use of the hypothesis. This study has been carried out in the near field of a 7[sdot ]62 cm circular air jet at a jet Reynolds number of 3[sdot ]2 x 104, where the coherent structures and their interactions have been organized through controlled excitation. Actual distributions of the structure properties have been obtained through phase-average hot-wire data, the measurements having been repeated at different spatial points over the extents of the structure crosssections at a fixed phase. The corresponding ‘spatial’ distributions of these properties obtained (by using the Taylor hypothesis) from the temporal data at appropriate phases and locations, show that the hypothesis works quite well for an isolated coherent structure if a constant convection velocity, equal to the structure centre velocity, is used in the hypothesis everywhere across the shear flow. The popular use of the local time-average or even the instantaneous streamwise velocity produces unacceptably large distortions. When structure interactions like pairing are involved, no convection velocity can be found with which the hypothesis works. Distributions of the terms in the Navier–Stokes equation contributing to the phase-average vorticity, but neglected by the hypothesis, have been quantitatively determined. These show that the terms associated with the background turbulence field, but not those associated with the coherent motion field, can be neglected. In particular, the pressure term due to the coherent motion field is large and cannot be neglected.