Collaborative Research: Multidimensional hydrodynamic studies of convection and mixing in stars, novae, and supernovae

该项目建立在全三维可压缩、多流体、湍流对流模拟的最新突破之上。对流几乎是绝热的（高佩莱特数），这是几乎所有恒星中对流的典型特征（除了恒星表面附近），直到它进入准静态湍流稳定状态才进行计算。这允许进行理论分析，显示如何改进传统的对流建模方法（混合长度理论）。这也表明了混合长度理论是如何能够很好地生存半个世纪的。新的结果几乎适用于恒星演化的所有阶段。一个新的特征是湍流夹带，这在气象学、海洋学和陆地实验中是众所周知的，但以前还没有应用于恒星的演化。三维模拟指出了恒星对流物理的一个更简单的公式，这个公式正在被纳入恒星演化代码中。在这里，博士将承担三个具体的项目。Arnett和Starrfield:(1)重新计算恒星的演化，从恒星诞生到死亡，形成超新星或白矮星，包括夹带和旋转；(2)扩展3D模拟，在不同的物理条件下测试这些新想法，包括旋转的影响；(3)使用经典新星的大量观测数据作为对流和剪切混合的理论测试平台。向经典新星的扩展涉及热核逃逸前的混合和逃逸过程中的混合。利用这些新方法将解决几个突出的问题，包括太阳丰度问题和日震学，经典新星的混合，大质量恒星的同位素产量，第一批恒星的混合及其对产量的影响，超新星祖先的非球形行为，以及成分梯度对太阳模拟的影响。这里开发的恒星演化软件和输入的数据将在一个网站上免费提供，供高级学生、教师和其他科学家使用，还有一套多维祖模型，用于模拟核心坍塌、热核超新星爆炸和新星。此外，样本演化序列（从0.7到200太阳质量）和同位素产量将可用于星系演化模型和陨石研究。提出了太阳对流区底部的模拟，这有助于扩展非弹性方法来处理非均匀流体。国家点火装置的激光实验目标设计将使用这个项目的模拟来测试超新星1987A的混合模型。

This project builds upon a recent breakthrough in the simulation of fully three-dimensional compressible, multifluid, turbulent convection. The convection is nearly adiabatic (high Peclet number), typical of almost all convection in stars (except near the stellar surface), and is calculated until it settles into a quasi-static turbulent steady state. This allows theoretical analysis which shows how to improve the conventional approach to modeling convection (mixing-length theory). It also shows how mixing-length theory could have worked well enough to survive for a half-century. The new results are applicable to almost all stages of stellar evolution. A new feature is turbulent entrainment, which is well known in meteorology, oceanography, and terrestrial experiments, but has not been previously applied to the evolution of stars. The three-dimensional simulations point to a simpler formulation of the stellar convection physics which is being incorporated into stellar evolutionary codes. Here, three specific projects will be undertaken by Drs. Arnett and Starrfield: (1) a recalculation of stellar evolution, from stellar birth to death with the formation of a supernova or a white dwarf, including entrainment and rotation, (2) an extension of the 3D simulations to test these new ideas in different physical conditions, including the effect of rotation, and (3) use of the extensive observational data on classical novae as a theoretical test bed for convective and shear mixing. Extension to classical novae involves both the mixing prior to the thermonuclear runaway and the mixing during the runaway itself. Several outstanding problems will be addressed using the new methods, including the solar abundance problem and helioseismology, mixing in classical novae, isotopic yields from massive stars, mixing in the first stars and its effect on yields, nonspherical behavior in supernova progenitors, and the effect of compositional gradients on solar simulations. The software for stellar evolution developed here and the input data, will be freely available on a website for use by advanced students, teachers, and other scientists, as will a set of multidimensional progenitor models for simulation of core collapse and thermonuclear supernova explosions, and novae. In addition, sample evolutionary sequences (from 0.7 to 200 Solar masses) and isotopic yields will be available for use in galactic evolutionary modeling and for meteoritic studies. Simulations of the bottom of the solar convection zone are proposed which should aid the extension of anelastic methods to deal with nonhomogeneous fluids. Target design for laser experiments at the National Ignition Facility will use simulations from this project to test mixing models for Supernova 1987A.