SHINE: Faster Boundary-Conforming Simulations of Solar Convection on Unstructured Grids

对空间天气的更快、更准确的预测需要建立太阳条件的模型。本项目通过推进可压缩高阶非结构谱差分(CHOUS)程序，发展了一个湍流太阳对流的计算模式。这个跨学科项目将支持两名研究生，其中包括一名女博士生和一名本科生研究助理。PI将与NOAA的空间天气预报中心以及NCAR的高海拔天文台合作，以开放源代码的形式更广泛地传播CHOUUS++。该项目加快了CHOUUS程序的计算效率，提高了其研究太阳对流的精度，具有前所未有的能力来捕捉太阳对流的层次性和非均质性，并进一步利用CHOUS的能力来揭示多尺度太阳对流，进而揭示密度层化和旋转影响下的湍流热对流的基本物理。合唱的出色并行效率使其能够达到捕捉太阳对流区(SCZ)强烈湍流性质所需的高计算分辨率。在本项目中，将在三个方面对CHOUUS进行改进：1)设计符合边界的超限映射，以完全消除等参数映射带来的数值误差；2)将空间精度从三阶(P2元素)提高到六阶(P5元素)；以及3)p精化和局部时间步长能力将在空间和时间上都具有更高的分辨率。由此产生的合唱++代码将比合唱快100倍以上。太阳大气中的湍流是由热对流驱动的，热对流将热量从太阳深处传输到表层，在那里辐射到太空。湍流对流反过来建立了调节太阳变率的平均流动和流体动力发电机作用。建立非均质性的一个基本因素是对流区内100万量级的气体密度的极端变化，这导致了动态长度和时间尺度上的相称差异。在上边界层辐射冷却的驱动下，较小的热羽流在更深的地方汇合成更大尺度的相干结构。这一巨大的动力学范围带来了巨大的建模挑战，它突破了计算流体动力学的极限，需要进行局部网格细化和本地时间步长进行并行计算。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Faster and more accurate predictions of space weather require model development of solar conditions. This project develops a computational model for turbulent solar convection by advancing the Compressible High-Order Unstructured Spectral difference (CHORUS) code. This interdisciplinary project will support two graduate students including a female Ph.D. student as well as an undergraduate research assistant. The PI will collaborate with NOAA’s Space Weather Prediction Center as well as NCAR’s High Altitude Observatory for broader dissemination of CHORUS++ as open-source code. This project accelerates the computational efficiency of CHORUS code and improves its accuracy for studying solar convection with an unprecedented capability to capture its hierarchical and inhomogeneous nature, and further exploits the capabilities of CHORUS to shed new light on multi-scale solar convection, and by extension, the fundamental physics of turbulent thermal convection under the influence of density stratification and rotation. The excellent parallel efficiency of CHORUS allows it to achieve the high computational resolution necessary to capture the intensely turbulent nature of the Sun’s convection zone (SCZ). In this project, CHORUS will be improved in three aspects: 1) a boundary- conforming transfinite mapping will be designed to completely remove numerical errors induced by iso-parametric mapping; 2) the order of accuracy in space will be improved from third-order (p2 elements) to sixth-order (p5 elements); and 3) p-refinements and local time stepping capabilities will be equipped for higher resolution in both space and time. The resultant CHORUS++ code will be over 100 times faster than CHORUS. Turbulence in the solar atmosphere is driven by thermal convection which transports heat from the deep solar interior to the surface layers where it is radiated into space. Turbulent convection in turn establishes mean flows and hydrodynamic dynamo action that regulates solar variability. An essential factor in establishing inhomogeneity is the extreme variation in gas density of order 1 million across the convection zone, which produces a commensurate disparity in the dynamical length and time scales. Small thermal plumes driven by radiative cooling in the upper boundary layer merge into larger-scale coherent structures deeper down. This vast dynamical range poses formidable modeling challenges that push the limits of computational fluid dynamics that require local mesh refinements and local time stepping for parallel computations.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.