论文标题
使用3D局部平均的湍流速度和标量场的间歇性
Intermittency of turbulent velocity and scalar fields using 3D local averaging
论文作者
论文摘要
提出了一种有效的方法，用于在球形子域中提取3D局部平均值，并应用用于研究各向同性湍流直接数值模拟中小规模速度和标量场的间歇性。我们专注于局部平均能量耗散速率，胚胎和标量耗散率的惯性尺度指数，与在均匀平均梯度的存在下相对应的对应于被动标量$θ$的混合。 Taylor-Scale Reynolds编号$R_λ$高达$ 1300 $，而Schmidt Number $ SC $最高$ 512 $（尽管以较小的$r_λ$为单位）。能量耗散速率的间歇性指数为$ \ \ \ 0.23 $，而esstrophy的间歇性指数则稍大。 $r_λ$的趋势表明，即使在极大的$r_λ$下，情况也是如此。标量耗散率的间歇性指数为$μ_θ\约0.35 $，$ sc = 1 $。这些发现与文献中先前报道的结果至关重要。我们进一步表明，$μ_θ$随着$ 1/\ log SC $的增加而单调降低，或者是弱功率定律，这表明$μ_θ\ to 0 $ aS $ sc \ to \ sc \ to \ infty $，重申了该限制中标量消散异常的最新结果。
An efficient approach for extracting 3D local averages in spherical subdomains is proposed and applied to study the intermittency of small-scale velocity and scalar fields in direct numerical simulations of isotropic turbulence. We focus on the inertial-range scaling exponents of locally averaged energy dissipation rate, enstrophy and scalar dissipation rate corresponding to the mixing of a passive scalar $θ$ in the presence of a uniform mean gradient. The Taylor-scale Reynolds number $R_λ$ goes up to $1300$, and the Schmidt number $Sc$ up to $512$ (albeit at smaller $R_λ$). The intermittency exponent of the energy dissipation rate is $μ\approx 0.23$, whereas that of enstrophy is slightly larger; trends with $R_λ$ suggest that this will be the case even at extremely large $R_λ$. The intermittency exponent of the scalar dissipation rate is $μ_θ\approx 0.35$ for $Sc=1$. These findings are in essential agreement with previously reported results in the literature. We further show that $μ_θ$ decreases monotonically with increasing $Sc$, either as $1/\log Sc$ or a weak power law, suggesting that $μ_θ\to 0$ as $Sc \to \infty$, reaffirming recent results on the breakdown of scalar dissipation anomaly in this limit.
