Turbulence-Flame Interactions in Type Ia Supernovae
Turbulence-Flame Interactions in Type Ia Supernovae
复制标题
Ia 型超新星中的湍流-火焰相互作用
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
M. Zingale
中科院分区：
文献类型：
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作者：
A. Aspden;John B. Bell;Marc Day;S. Woosley;M. Zingale
Ia型超新星(SNE Ia)涉及的时间和长度尺度范围很大，需要使用火焰模型。作为探索各种火焰模型选择的前奏，我们在本文中考虑了在超新星环境中对核火焰小尺度动力学的高分辨率三维模拟，在这种模拟中，火焰结构的细节被完全解决。所研究的密度范围为(1-8)×107g cm−3，从层流火焰区过渡到小尺度湍流扰乱火焰的分布式燃烧区。低马赫数算法的使用有助于准确解析火焰和无粘动能叶栅的热结构，同时隐含了网格尺度截止处的动能耗散。对于能量特征为SneIa的各向同性Kolmogorov湍流背景，我们得到了1到3×107g cm−3之间的跃迁密度，燃烧的性质发生了质的变化。每增加1×107g cm−3，在火焰尺度上，湍流平流就超过了传导和辐射的能量扩散。因此，有效的刘易斯数接近于1。也就是说，火焰类似于层流火焰，但通过有效扩散系数dT∼u‘l进行湍流展宽，其中u’是湍流强度，L是积分尺度。对于真实超新星的较大整体尺度特征，火焰结构预计将变得复杂和不稳定。文中还讨论了可能过渡到爆轰的含义。
The large range of time and length scales involved in Type Ia supernovae (SNe Ia) requires the use of flame models. As a prelude to exploring various options for flame models, we consider in this paper high-resolution, three-dimensional simulations of the small-scale dynamics of nuclear flames in the supernova environment in which the details of the flame structure are fully resolved. The range of densities examined, (1–8) × 107 g cm−3, spans the transition from the laminar flamelet regime to the distributed burning regime where small-scale turbulence disrupts the flame. The use of a low Mach number algorithm facilitates the accurate resolution of the thermal structure of the flame and the inviscid turbulent kinetic energy cascade, while implicitly incorporating kinetic energy dissipation at the grid-scale cutoff. For an assumed background of isotropic Kolmogorov turbulence with an energy characteristic of SNe Ia, we find a transition density between 1 and 3 × 107 g cm−3, where the nature of the burning changes qualitatively. By 1 × 107 g cm−3, energy diffusion by conduction and radiation is exceeded, on the flame scale, by turbulent advection. As a result, the effective Lewis number approaches unity. That is, the flame resembles a laminar flame but is turbulently broadened with an effective diffusion coefficient, DT ∼ u′l, where u′ is the turbulent intensity and l is the integral scale. For the larger integral scales characteristic of a real supernova, the flame structure is predicted to become complex and unsteady. Implications for a possible transition to detonation are discussed.