Surface morphology and inner fractal cutoff scale of spherical turbulent premixed flames in decaying isotropic turbulence
Surface morphology and inner fractal cutoff scale of spherical turbulent premixed flames in decaying isotropic turbulence
复制标题
衰减各向同性湍流中球形湍流预混火焰的表面形貌和内分形截止尺度
DOI：
10.1016/j.proci.2020.06.117
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发表时间：
2020
影响因子：
3.4
通讯作者：
Bisetti, Fabrizio
中科院分区：
文献类型：
--
作者：
Kulkarni, Tejas;Bisetti, Fabrizio
湍流预混火焰表面在有限尺度范围内具有分形特征，分形维数和内截止尺度是湍流燃烧分形闭合的重要组成部分。在这样的封闭，表面积的估计是敏感的内分形截止尺度，其建模仍然不清楚，实验和数值矛盾的证据存在的值。在这项工作中，我们分析的数据从六个直接数值模拟的球形膨胀湍流预混火焰在不同的雷诺数和Karlovitz数。火焰在衰减的各向同性湍流中传播，并落入小火焰区域。过去的初始瞬态，我们发现，分形维数达到2.3和2.4之间的渐近值与以前的结果在类似的条件下。雷诺数和Karlovitz数上的分形维数的一个小的依赖性观察和解释的雷诺数和狭窄的惯性和分形范围的相对较低的值。内分形截断尺度Δ* 的尺度为Δ*/l <$Re λ− 1.14，其中l是湍流的积分尺度，Re λ是基于反应物侧湍流中计算的泰勒微观尺度的雷诺数。在本研究中考虑的值范围内，缩放是稳健的，对Karlovitz数不敏感。一个重要的含义是，比值Δ*/η随着雷诺数（η是柯尔莫哥洛夫尺度）而增长，尽管速度相当慢，这可以解释4≤ Δ*/η≤ 10的广泛观察结果。这表明，Δ* 虽然小于λ，但不是火焰表面的耗散长度尺度，并且仅由η标度。最后，确定了一个耗散阈值尺度，该尺度在η归一化后保持恒定。
The surface of turbulent premixed flames is fractal within a finite range of scales and the fractal dimension and inner cutoff scale are key components of fractal turbulent combustion closures. In such closures, the estimate for the surface area is sensitive to the value of the inner fractal cutoff scale, whose modeling remains unclear and for which both experimental and numerical contradictory evidence exists. In this work, we analyze data from six direct numerical simulations of spherically expanding turbulent premixed flames at varying Reynolds and Karlovitz numbers. The flames propagate in decaying isotropic turbulence and fall in the flamelet regime. Past an initial transient, we find that the fractal dimension reaches an asymptotic value between 2.3 and 2.4 in good agreement with previous results at similar conditions. A minor dependence of the fractal dimension on the Reynolds and Karlovitz numbers is observed and explained by the relatively low values of the Reynolds number and narrow inertial and fractal ranges. The inner fractal cutoff scale Δ* is found to scale as Δ*/l∼ Re λ− 1.14, where l is the integral scale of turbulence and Re λ is the Reynolds number based on the Taylor micro-scale computed in the turbulence on the reactants’ side. The scaling is robust and insensitive to the Karlovitz number over the range of values considered in this study. An important implication is that the ratio Δ*/η grows with Reynolds number (η is the Kolmogorov scale), albeit at a rather slow rate that may explain the widespread observation that 4≤ Δ*/η≤ 10. This suggests that Δ*, although smaller than λ, is not a dissipative length scale for the flame surface and scaled solely by η. Finally, a dissipative threshold scale that remains constant once normalized by η is identified.
涡流熄灭火焰的图像 - 量化湍流燃烧状态
影响因子：
4.4
作者：
W. Roberts;J. Driscoll;M. C. Drake;L. Goss
通讯作者：
L. Goss
影响因子：
3.4
作者：
S. Luca;A. Attili;E. Lo Schiavo;F. Creta;F. Bisetti
通讯作者：
S. Luca;A. Attili;E. Lo Schiavo;F. Creta;F. Bisetti