Numerical analysis of particle-turbulence interaction in high-speed gas flows

高速气流与分散的固体颗粒或液滴的相互作用在各种地球物理、天体物理和技术过程中起着决定性的作用。这些例子包括火山爆发、超新星的形成、表面涂层的冷喷涂以及超音速内燃机。这些多相系统的特征是气相湍流、颗粒动力学、热传递和冲击波等可压缩效应的复杂相互作用。尽管应用种类繁多，但对这些流动中颗粒-湍流相互作用的基本机制仍知之甚少。大量涉及的物理效应以及不同长度和时间尺度的广泛范围加剧了对这些系统的数值分析。同样，这些条件通常会妨碍详细的实验测量。基础知识的缺乏阻碍了颗粒和湍流模型的发展；然而，在上述应用中，准确的模型对于预测模拟是必不可少的。例如，由于目前缺乏描述气体、岩浆和岩石碎片以极高速度相互作用的模型，火山爆发对附近人口、航空和全球气候的影响几乎不可预测。在这个项目中，将对存在显著可压缩效应和热传递的颗粒-湍流相互作用进行新的高分辨率数值分析，以使模型开发和验证成为可能。研究了各向同性湍流的正则流问题，有助于理解决定多相相互作用的基本机制。利用申请人最近开发的一种有效的数值方法，每个颗粒周围的湍流运动和流场将通过物理守恒定律得到完全求解。这种方法产生了对多相相互作用的准确描述，这是以前没有关于这类流动的文献记载的。这些数据将为粒子和可压缩湍流的相互影响提供新的见解，例如，详细描述这两个阶段的动量和能量平衡。通过与这些参考解决方案的比较，将分析现有的、但从未得到验证的粒子模型的准确性。此外，还将在已有知识和机械方法的基础上开发新的模型。模型的彻底定义及其有效性范围对于应用模拟的准确性是至关重要的。

The interaction of high-speed gas flows with dispersed solid particles or droplets plays a decisive role in various geophysical, astrophysical, and technical processes. Examples include explosive volcanic eruptions, the formation of supernovae, cold spraying to deposit surface coatings, and supersonic combustion engines. These multiphase systems are characterized by a complex interplay of gas-phase turbulence, particle dynamics, heat transfer, and compressibility effects such as shock waves. Despite the large variety of applications, the fundamental mechanisms of particle-turbulence interaction in these flows are still poorly understood. The large number of involved physical effects and the vast range of different length and time scales exacerbate numerical analyses of these systems. Similarly, these conditions often prevent detailed experimental measurements. The lack of fundamental understanding inhibits the development of particle and turbulence models; however, accurate models are indispensable for predictive simulations in the above mentioned applications. As an example, the impact of explosive volcanic eruptions on the nearby population, aviation, and global climate is barely predictable due to the current lack of models describing the interaction of gas, magma, and rock fragments at very high velocities.In this project, novel highly-resolved numerical analyses of particle-turbulence interaction in the presence of pronounced compressibility effects and heat transfer will be conducted to enable model development and validation. The canonical flow problem of isotropic turbulence is considered which facilitates to gain understanding of the fundamental mechanisms which determine the multiphase interaction. Using an efficient numerical method recently developed by the applicant, the turbulent motion and the flow field around each particle will be fully resolved via the physical conservation laws. This approach yields an accurate description of the multiphase interaction which has not been documented for this class of flows previously. The data will provide new insight into the mutual influence of particles and compressible turbulence, e.g., detailing the momentum and energy balances of both phases. By comparison with these reference solutions, the accuracy of existing, yet never validated particle models will be analyzed. Furthermore, based on the gained knowledge and mechanistic approaches, new models will be developed. The thorough definition of the models and their range of validity is crucial for the accuracy of applied simulations.