Dissipation-range geometry and scalar spectra in sheared stratified turbulence
Dissipation-range geometry and scalar spectra in sheared stratified turbulence
复制标题
剪切分层湍流中的耗散范围几何和标量谱
DOI：
10.1017/s0022112099006734
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发表时间：
1999
影响因子：
3.7
通讯作者：
W. Smyth
中科院分区：
文献类型：
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作者：
W. Smyth
采用直接数值模拟的方法，对层状剪切流动中Kelvin-Helmholtz不稳定性引起的湍流进行了数值模拟，考察了不同流型下的耗散范围的几何形状。由于浮力和剪切雷诺数的增加量化了耗散范围内的各向同性程度，对齐统计从平行剪切流的特征演变为先前在定常、各向同性、均匀湍流研究中发现的那些(例如Ashurst等人)。1987年；她等人。1991年；Tsinober等人。(1992年)。分析得出了标量梯度平均压缩比的极限值，在足够高的雷诺数下，该极限值有望成为所有湍流的特征。我主要关注的是在Batchelor(1959)和Kraichnan(1968)关于被动标量谱的理论形式中出现的常数Q的值。考虑到随时间变化的应变的影响，我提出了一个修正的Q估计，表示为QE，它似乎比以前的理论估计更符合从模拟和观测得出的频谱形状。修正后的估计值为QE=7.3±4，当浮力雷诺数超过O(102)时，QE将是有效的。考虑了间歇性影响的Kraichnan(1968)谱形式比Batchelor(1959)谱形式更符合DNS结果。
Direct numerical simulations of turbulence resulting from Kelvin–Helmholtz instability in stratified shear flow are used to examine the geometry of the dissipation range in a variety of flow regimes. As the buoyancy and shear Reynolds numbers that quantify the degree of isotropy in the dissipation range increase, alignment statistics evolve from those characteristic of parallel shear flow to those found previously in studies of stationary, isotropic, homogeneous turbulence (e.g. Ashurst et al. 1987; She et al. 1991; Tsinober et al. 1992). The analysis yields a limiting value for the mean compression rate of scalar gradients that is expected to be characteristic of all turbulent flows at sufficiently high Reynolds number. My main focus is the value of the constant q that appears in both the Batchelor (1959) and Kraichnan (1968) theoretical forms for the passive scalar spectrum. Taking account of the effects of time-dependent strain, I propose a revised estimate of q, denoted qe, which appears to agree with spectral shapes derived from simulations and observations better than do previous theoretical estimates. The revised estimate is qe = 7.3±4, and is expected to be valid whenever the buoyancy Reynolds number exceeds O(102). The Kraichnan (1968) spectral form, in which effects of intermittency are accounted for, provides a better fit to the DNS results than does the Batchelor (1959) form.