Integrated Variable Fidelity Eddy Capturing Approach for Turbulent Flow Simulations

用于湍流模拟的集成可变保真度涡流捕获方法

• 批准号: 0756046
• 负责人: Oleg Vasilyev
• 金额: $ 24万
• 依托单位: University of Colorado at Boulder
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-08-01 至 2011-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0756046&HistoricalAwards=false
• 关键词: Integrated; Variable; Fidelity; Eddy; Capturing

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.

CBET-0756046Vasilyv这项研究解决了长期以来对能够对复杂几何形状的非定常湍流进行变保真数值模拟的集成自适应涡流捕获方法的需求。最近，数值模拟与实验的详细比较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)对于强湍流的计算成本过高，解决所有主导流动物理的涡流的唯一可行的方法是大涡模拟(LES)。然而，目前的大涡模拟方法充其量依赖于一种带状网格自适应策略来尝试最小化解决大涡的计算成本。虽然这些方法是对常规网格的改进，但它们不能解决空间间歇性相干涡旋的高波数分量，这些涡流是湍流的典型特征。同时，在间歇性相干涡旋之间的区域内，流动被过度分辨。最近对大涡模拟方法的改进，即PI最近提出的随机相干自适应大涡模拟(Scale)方法，通过使用动态网格自适应策略来解决最能量相干结构的问题，从而解决了传统大涡模拟方法的缺点。这种新的方法现在已经证明了动态解析和跟踪的能力。相干涡旋中能量最大的部分，同时使用场压缩，导致类似于LES的自由度数量的减少。这一思想将通过应用空间可变的小波阈值策略进一步发展，以确保仅对湍流动能、次网格尺度耗散或其他统计量的先验指定分数进行解析。在这种策略下，基于自适应小波的数值模拟(WDNS)、相干涡旋模拟(CVS)和尺度模式之间的转换是很自然的：随着湍流动能或亚网格耗散所占比例的增加，尺度模式对于CVS转换为亚网格模式，而对于WDNS方法则为无模式。这将为综合自适应变保真度(WDNS/CVS/Scale)涡流捕获方法的新策略奠定基础。最后，为了使计划的方法成为实际的工程工具，它将与布林克曼惩罚相结合，以强制实施任意复杂的坚实边界。将这种基于小波的动态网格自适应策略与Brinkman惩罚相结合的一个独特优势是能够将边界条件强制到指定的精度，而不需要大量的计算开销。这种结合的方法将显著减少工时(与繁琐的网格生成相关)和计算成本。该项目的最终目的是教育和传播新制定的方法，并分发将作为该项目一部分开发的软件工具，供科学界包括政府实验室广泛使用。