用深度学习从模拟数据中训练稳定湍流模型,适配不同数值格式。
Deep Learning of Solver-Aware Turbulence Closures from Nudged LES Dynamics

- 基于连续数据同化框架,无需修改或反向传播求解器。
- 仅用稀疏DNS数据训练,恢复的统计量保持稳定且准确。
- 显式条件化数值格式,可适应不同离散化带来的误差。
微分物理范式可作为后验方法,将神经网络参数化直接嵌入求解器中,并利用可能稀疏的目标数据进行优化,以发现湍流闭合模型。这解决了先验学习中的关键限制:先验学习通常使用直接数值模拟(DNS)数据近似亚格子应力,假设存在低通滤波,但实际数值离散化和粗粒化效应与该假设不一致,导致训练出的闭合模型在部署时不稳定。相比之下,虽然后验学习在部署中通常稳定,但需对大涡模拟(LES)求解器进行反向传播,计算成本高昂;且由于需大幅修改现有求解器,难以广泛适用。此外,两种方法在跨不同数值方案时泛化能力受限。本文提出一种基于连续数据同化框架的深度学习湍流闭合建模方法,可在不修改或对求解器反向传播的前提下,仅用稀疏观测的DNS数据实现先验训练,同时保证部署时的稳定性与不变统计量的恢复。我们通过二维和三维经典算例验证框架,结果表明所学修正项能系统性追踪粗网格求解器的离散化误差。
原文摘要 · Abstract (English)
The differentiable physics paradigm may be leveraged as an a-posteriori approach for discovering turbulence closure models by embedding a neural network parameterization directly inside the solver and optimizing it given potentially sparse target data. This addresses a key limitation of a-priori learning where direct numerical simulation (DNS) data is used to approximate the subgrid stress with the assumption of a low-pass filter. Closures trained in this a-priori manner frequently lead to unstable deployments due to the mismatch between the assumed filter and the effect of numerical discretizations and coarse-graining. In comparison, while typically stable during deployment, a-posteriori learning incurs high computational costs due to the need to backpropagate through a large eddy simulation (LES) solver. Furthermore, a-posteriori methods are challenging to apply broadly since they require significant modification of existing solvers. Finally, both approaches are limited when generalization is desired across different numerical schemes with their implicit filtering characteristics. In this work, we present a deep-learning approach for turbulence closure modeling built on the continuous data assimilation framework. Our approach enables the a-priori training of closures using sparsely observed DNS data without modifying or differentiating through the LES solver, while preserving stability during deployment for the recovery of invariant statistics. We focus on the model's ability to adapt to different discretizations by explicitly conditioning it on the numerical scheme. We use two- and three-dimensional canonical cases to test our framework and show that the learned correction systematically tracks the discretization error of the coarse solver.
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