Integrated Variable Fidelity Eddy Capturing Approach for Turbulent Flow Simulations

CBET-0756046 Vasilyev本研究解决了长期以来对集成自适应涡流捕获方法的需求，该方法能够对复杂几何形状中的非定常湍流进行可变保真度数值模拟。最近详细的数值模拟与实验的比较已经清楚地表明了捕捉主导的三维湍流特征的重要性。由于直接数值模拟（DNS）的高湍流流动的计算成本过高，唯一的计算可行的替代方案，以解决所有的漩涡，占主导地位的流动物理是大涡模拟（LES）。然而，目前的LES方法依赖于，在最好的，分区网格自适应策略，试图最大限度地减少计算成本，解决大涡。虽然改进了规则的网格，这些方法无法解决高波数组件的空间间歇性相干涡流，代表湍流。同时，在间歇相干涡之间的区域中，流动是过分辨的。最近改进的LES方法，即随机相干自适应大涡模拟（SCALES）的方法，最近开发的PI，解决了传统LES方法的缺点，通过使用动态网格自适应策略，解决了最有力的相干结构。这种新的方法，现在已经证明了动态解决和？跟踪？的相干涡流的最有力的部分，而使用的字段压缩，导致在自由度的数量减少类似LES。这个想法是采取一个步骤，通过应用空间可变的小波阈值策略，以确保只有一个先验指定的分数的湍流动能，亚网格尺度耗散或其他统计量的解决。采用这种策略，自适应小波基DNS（WDNS），相干涡模拟（CVS）和SCALES制度之间的过渡是自然的：SCALES模型切换到亚网格尺度模型的CVS没有模型的WDNS方法作为解决湍流动能或亚网格尺度耗散的百分比增加。这将为综合自适应可变保真度（WDNS/CVS/SCALES）涡流捕获方法的新策略奠定基础。最后，为了使计划方法成为实用的工程工具，它将与Brinkman惩罚相结合，以强制任意复杂性的坚实边界。将这种基于动态小波的网格自适应策略与Brinkman惩罚相结合的独特优势是能够在没有显著计算开销的情况下将边界条件强制执行到指定精度。结合的方法将允许显着降低成本的工时（与繁琐的网格生成）和计算成本。该项目的最终目的是教育和传播新开发的方法，并分发作为项目一部分开发的软件工具，供包括政府实验室在内的科学界广泛使用。

CBET-0756046VasilyevThis study addresses the longstanding need for an integrated adaptive eddy capturing approach capable of performing variable fidelity numerical simulations of unsteady turbulent flows in complex geometries. Recent detailed comparison of numerical simulations with experiments has clearly shown the importance of capturing the dominant three-dimensional turbulent flow features. Due to prohibitive computational cost of the Direct Numerical Simulations (DNS) for highly turbulent flows, the only computationally feasible alternative to resolve all eddies that dominate flow physics is Large Eddy Simulation (LES). However, current LES methodologies rely on, at best, a zonal grid adaptation strategy to attempt to minimize computational cost in resolving large eddies. While an improvement over regular grids, these methodologies fail to resolve the high wave-number components of the spatially intermittent coherent eddies that typify turbulent flows. At the same time, the flow is over-resolved in regions between the intermittent coherent eddies. Recent improvement of the LES methodology, namely the Stochastic Coherent Adaptive Large Eddy Simulation (SCALES) approach, recently developed by PI, addresses shortcomings of traditional LES approaches by using a dynamic grid adaptation strategy that resolves the most energetic coherent structures. This novel methodology has now demonstrated the ability to dynamically resolve and ?track? the most energetic part of the coherent eddies, while using a field compression that results in a reduction in the number of degrees of freedom similar to LES. This idea is to be taken one step further by applying spatially variable wavelet thresholding strategy to ensure that only a priori specified fraction of turbulent kinetic energy, subgrid scale dissipation or other statistical quantities are resolved. With such a strategy the transition between adaptive wavelet based DNS (WDNS), Coherent Vortex Simulation (CVS), and SCALES regimes is natural: the SCALES models switch to subgrid scale model for CVS to no model for WDNS approach as the percentage of the resolved turbulent kinetic energy or subgrid scale dissipation increases. This will form a basis for the new strategy of the integrated adaptive variable fidelity (WDNS/CVS/SCALES) eddy capturing approach. Finally, to make a planned methodology a practical engineering tool, it will be combined with Brinkman penalization to enforce solid boundaries of arbitrary complexity. A unique advantage of combining this dynamic wavelet-based grid adaptation strategy with Brinkman penalization is the ability to enforce boundary conditions to a specified precision without a significant computational overhead. The combined approach will allow for a significant cost reduction in man hours (associated with tedious grid generation) and computational costs. The final aim of this project is in education and dissemination of the newly developed approach and in distribution of the software tools to be developed as a part of the project for the wide use by the scientific community including government laboratories.