用物理方程特征识别流场动态集群,揭示流动演化规律。
Equation-informed data-driven identification of flow budgets and dynamics
- 基于控制方程构造点级动力学特征,量化各物理项贡献。
- 在圆柱绕流与湍流数据中成功识别出稳定、瞬态与振荡流区。
- 支持欧拉与拉格朗日框架,可追踪集群随时间演变过程。
计算流体动力学(CFD)在工程建模中不可或缺,能显著减少对物理原型与试验的需求。针对系统复杂度不同,可采用从低到高保真度的模型进行预测,实现大幅加速。然而,模型选择依赖于对实际流动动力学的准确理解。正确识别具有相同动力学特性的流动区域或簇,仍是研究难点。本文提出一种新型混合流场聚类方法:通过稀疏非线性动力系统识别(SINDy)方法对每个样本点的时间演化数据进行逐点处理,构造基于方程的特征(即各项对局部动力学的贡献预算)。随后利用Girvan-Newman算法进行方程驱动聚类,实现对共享相同物理动态的社区检测。该方法在欧拉与拉格朗日框架中均实现。在拉格朗日框架下,对每个点的轨迹进行聚类,可表征集群随时间的变化。算法在圆柱绕流测试中表现良好,清晰展示尾流从稳态、瞬态到振荡解的演化过程。在湍流数据中成功识别出两个明确分离的集群,并重建了其时序演化特征。
原文摘要 · Abstract (English)
Computational Fluid Dynamics (CFD) is an indispensable method of fluid modelling in engineering applications, reducing the need for physical prototypes and testing for tasks such as design optimisation and performance analysis. Depending on the complexity of the system under consideration, models ranging from low to high fidelity can be used for prediction, allowing significant speed-up. However, the choice of model requires information about the actual dynamics of the flow regime. Correctly identifying the regions/clusters of flow that share the same dynamics has been a challenging research topic to date. In this study, we propose a novel hybrid approach to flow clustering. It consists of characterising each sample point of the system with equation-based features, i.e. features are budgets that represent the contribution of each term from the original governing equation to the local dynamics at each sample point. This was achieved by applying the Sparse Identification of Nonlinear Dynamical systems (SINDy) method pointwise to time evolution data. The method proceeds with equation-based clustering using the Girvan-Newman algorithm. This allows the detection of communities that share the same physical dynamics. The algorithm is implemented in both Eulerian and Lagrangian frameworks. In the Lagrangian, i.e. dynamic approach, the clustering is performed on the trajectory of each point, allowing the change of clusters to be represented also in time. The performance of the algorithm is first tested on a flow around a cylinder. The construction of the dynamic clusters in this test case clearly shows the evolution of the wake from the steady state solution through the transient to the oscillatory solution. Dynamic clustering was then successfully tested on turbulent flow data. Two distinct and well-defined clusters were identified and their temporal evolution was reconstructed.
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