采用直接数值模拟方法,对具有平均标量梯度的被动标量场在稳定、均匀各向同性湍流中的统计特性进行了研究(计算Reλ为25和48,Pr数从0.3到4.0).模拟结果表明:标量的概率密度函数是高斯分布的;标量耗散率的概率分布是不对称性的,在它的左枝还存在明显的拖尾现象,并非对数正态分布;在Re数相同的情况下,随着Pr数的增加,沿着平均标量梯度方向上的标量梯度其概率分布的偏斜度是减少的,反映出回归各向同性的趋势,而且在以涡量为条件的标量梯度的偏斜度变化曲线中发现涡量影响的饱和现象,我们认为这是由于涡量通过对标量场小尺度结构进行旋转作用来影响标量场的结果.
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