各向同性衰变湍流的直接数值模拟研究

该文对各向同性衰变湍流进行了直接数值模拟。获得了衰变湍流的瞬态特性,研究了在谱空间以波数为半径的不同球面处能量分布的特性。计算结果显示:在谱空间的每一个球面或波数处,动能与拟涡能都有一定的分布范围。在大部分的波数处,能量的分布跨越了几个量级。在同一动能与拟涡能处,波数的分布也有着较大的跨度。在相同的无量纲波数处,动能与拟涡能的概率密度函数(PDF)有着相同的分布形状,且不随湍流的衰减而改变。当运动尺度远离Kolmogorov尺度时,不同波数处拟涡能的PDF 分布形状有着较好的一致性。当运动尺度逐渐接近Kolmogorov 尺度时,PDF 分布的形状逐渐发生变化,PDF 的峰值向低拟涡能处移动且峰值增大,高拟涡能区域的PDF值有所降低。

DIRECT NUMERICAL SIMULATION OF ISOTROPIC DECAYING TURBULENCE

This paper presents a direct numerical simulation of an isotropic decaying turbulence.The instantaneous characteristics of the decaying turbulence are obtained.The energy distributions are studied on different spherical surfaces with wave number as radius in spectral space.The results show that both values taken by kinetic energy and enstrophy have certain ranges at each wave number.They cover several orders of magnitude at most of wave numbers.The wave numbers also have wide ranges at each value of kinetic energy or enstrophy.The probability density functions(PDF) for kinetic energy and enstrophy share the same distribution at the same non-dimensional wave number.They exhibit almost no changes along with the decay of turbulence.The PDFs for the enstrophy nearly have the same distribution at different wave numbers when the length scales are far away from the Kolmogorov scale.When the length scales gradually approach to the Kolmogorov scale,the peak value of the PDF increases and moves to the low enstrophy region.The values of the PDF decrease in the high enstrophy region.