Flow Dynamics in Buoyancy-Driven Variable-Density Turbulent Mixing with Compressibility Effects

一般来说，在超音速到高超声速燃烧和推进、聚变技术和天体物理学中观察到的复杂流动涉及多种物质混合，跨越广泛的空间和时间尺度。参与这种流动的流体有很大范围的摩尔质量，在许多情况下，这种流动是高度可压缩的。对于目前的工程工具来说，预测由于可压缩性和材料性质变化而产生的关键流动物理仍然是一个挑战。更深入地了解这些对湍流的影响将大大提高我们对流动物理进行精确建模的能力，例如复杂多物质流动中发生的湍流混合的速度，并以较低的计算成本执行此类流动的数值模拟。这些能力的提高将直接影响航天、能源、国防等领域许多高科技产品的改进和发展。因此，研究的重点是量化大摩尔质量比和可压缩性对重力驱动湍流流动的耦合影响。该项目还将通过为本科生和研究生课程编写内容来提供教育内容。它还将支持外展活动，以提高本地中学生对流体动力学和湍流的兴趣，并在更广泛的范围内促进STEM。迄今为止，多物质湍流的研究主要是利用准不可压缩和Boussinesq流动，材料性质的变化很小。该项目旨在描述流体可压缩性对Rayleigh-Taylor不稳定湍流混合的影响，该混合具有超出Boussinesq近似和不可压缩假设的大密度变化。新的直接数值模拟浮力驱动的流动，解决所有的空间和时间尺度将执行大密度比(2)与高度可压缩的流体使用自适应网格加密，以优化配置计算资源。将开发独特的统计工具来量化非Boussinesq湍流可压缩混合动力学。所提出的模拟和统计分析将被用来建立对非Boussinesq流动的湍流转变的更深层次的理解，特别是可压缩主动标量混合的小尺度流动拓扑。此外，本研究的结果有望为新的亚网格尺度的模型和策略提供参考，以降低多物理复杂流体流动模拟的计算成本，并验证针对这些复杂流动的降阶模型。该项目由流体动力学计划和既定的激励竞争研究计划(EPSCoR)共同资助。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。

In general, complex flows - those observed in supersonic-to-hypersonic combustion and propulsion, fusion technologies, and astrophysics - involve multi-material mixing and span a broad range of space and time scales. Fluids participating in such flows have a wide range of molar masses, and in many cases, the flow is highly compressible. It is still a challenge for current engineering tools to predict the key flow physics that arise due to the compressibility and large material property variations. A stronger fundamental understanding of these effects on turbulent flows will significantly increase our ability to model the flow physics accurately, such as the rate of turbulent mixing that occurs in complex multi-material flows, and to perform numerical simulations of such flows with a decreased computational expense. These gained abilities will have a direct impact on the improvement and development of many high-tech products in the space, energy, and defense industries. Therefore, the focus of the proposed study is to quantify the coupled large molar-mass ratio and compressibility effects on the gravitationally driven turbulent flows. The project will also deliver an educational component by generating content for undergraduate- and graduate-level courses. It will also support outreach activities to promote interest in fluid dynamics and turbulence, and more broadly in STEM among local middle-school students.Multi-material turbulence has so far mostly been studied with quasi-incompressible and Boussinesq flows with small variations in material properties. The proposed project aims to describe flow compressibility effects on Rayleigh-Taylor unstable turbulent mixing with large density variations beyond the Boussinesq approximation and the incompressible assumption. Novel direct numerical simulations of buoyancy-driven flow that resolve all spatial and temporal scales will be performed at large density ratios (2) with highly compressible fluids using the adaptive mesh refinement to optimally deploy computational resources. Unique statistical tools will be developed to quantify the non-Boussinesq turbulent compressible mixing dynamics. The proposed simulations and statistical analyses will be used to establish a deeper understanding of turbulence transition for non-Boussinesq flows, and in particular, the small-scale flow topology of the compressible active-scalar mixing. In addition, the findings of this research are expected to inform new sub-grid-scale models and strategies to decrease the computational cost of the multi-physics complex fluid-flow simulations and validate the reduced-order models for these complex flows. This project is jointly funded by Fluid Dynamics program and the Established Program to Stimulate Competitive Research (EPSCoR).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.