Direct numerical simulations of the turbulence evolution in a uniformly sheared and stably stratified flow
Direct numerical simulations of the turbulence evolution in a uniformly sheared and stably stratified flow
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DOI：
10.1017/s0022112097005478
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发表时间：
1997-07
影响因子：
3.7
通讯作者：
F. Jacobitz;S. Sarkar;C. W. Atta
中科院分区：
文献类型：
--
作者：
F. Jacobitz;S. Sarkar;C. W. Atta
采用直接数值模拟方法研究了均匀剪切稳定分层流中湍流的演化。空间离散采用谱配置法，时间求解采用三阶龙格-库塔格式。湍流演化至少强烈地依赖于三个参数：梯度Richardson数Ri、Taylor微尺度雷诺数Re λ的初始值和剪切数SK/<ε的初始值。每个参数的影响进行单独研究，而其余参数保持不变。湍流动能K的演化近似遵循指数规律。剪切数SK/<ε（其影响在以前的研究中尚未研究）被发现对湍流演化具有很强的非单调影响。剪切数越大，湍流动能的最终增长率就越大。雷诺数Re λ的变化表明，在所研究的Re λ范围的较高端，湍流增长率趋于对Re λ不敏感。给出了分离湍流动能K的渐近增长和渐近衰减的临界Richardson数Ricr与雷诺数Re λ和剪切数SK/<ε初值的关系。结果表明，由于临界Richardson数对雷诺数和剪切数有很强的依赖性，在我们的DNS中，临界Richardson数在0.04 <Ricr <0.17的范围内变化。
Direct numerical simulations (DNS) are performed to investigate the evolution of turbulence in a uniformly sheared and stably stratified flow. The spatial discretization is accomplished by a spectral collocation method, and the solution is advanced in time with a third-order Runge–Kutta scheme. The turbulence evolution is found to depend strongly on at least three parameters: the gradient Richardson number Ri, the initial value of the Taylor microscale Reynolds number Reλ, and the initial value of the shear number SK/<ε. The effect of each parameter is individually studied while the remaining parameters are kept constant. The evolution of the turbulent kinetic energy K is found to follow approximately an exponential law. The shear number SK/<ε, whose effect has not been investigated in previous studies, was found to have a strong non-monotone influence on the turbulence evolution. Larger values of the shear number do not necessarily lead to a larger value of the eventual growth rate of the turbulent kinetic energy. Variation of the Reynolds number Reλ indicated that the turbulence growth rate tends to become insensitive to Reλ at the higher end of the Reλ range studied here. The dependence of the critical Richardson number Ricr, which separates asymptotic growth of the turbulent kinetic energy K from asymptotic decay, on the initial values of the Reynolds number Reλ and the shear number SK/<ε was also obtained. It was found that the critical Richardson number varied over the range 0.04<Ricr<0.17 in our DNS due to its strong dependence on Reynolds and shear numbers.