We investigate numerically the three-dimensional (3D) flow around a squareback Ahmed body at Reynolds number $\text{Re}={10}^4$. Proper orthogonal decomposition (POD) is applied to a symmetry-augmented database in order to describe and model the flow dynamics. Comparison with experiments at a higher Reynolds number in a plane section of the near wake at midheight shows that the simulation captures several features of the experimental flow, in particular the antisymmetric quasisteady deviation mode. 3D POD analysis allows us to classify the different physical processes in terms of mode contribution to the kinetic energy over the entire domain. It is found that the dominant fluctuating mode on the entire domain corresponds to the 3D quasisteady wake deviation, and that its amplitude is well estimated from 2D near-wake data. The next most energetic flow fluctuations consist of vortex shedding and bubble pumping mechanisms. It is found that the amplitude of the deviation is negatively correlated with the intensity of the vortex shedding in the spanwise direction and the suction drag coefficient. Finally, we find that despite the slow convergence of the decomposition, a POD-based low-dimensional model reproduces the dynamics of the wake deviation observed experimentally, as well as the main characteristics of the global modes identified in the simulation.

中文翻译：

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方背Ahmed身后的尾流偏差的正确正交分解分析和建模

我们以雷诺数以数字方式研究围绕方背Ahmed体的三维（3D）流动 $\text{回覆}={10}^4$。适当的正交分解（POD）应用于对称性增强的数据库，以描述和建模流动动力学。与中高度近尾的平面截面中较高雷诺数下的实验进行比较表明，该模拟捕获了实验流的多个特征，特别是反对称准稳态偏差模式。3D POD分析使我们可以根据模式对整个域中动能的贡献来对不同的物理过程进行分类。发现整个域上的主要波动模式对应于3D准稳态苏醒偏差，并且其振幅可以从2D近苏醒数据中很好地估计出来。第二个最活跃的流量波动包括涡流脱落和气泡泵送机制。发现偏差的幅度与在翼展方向上涡旋脱落的强度和吸阻力系数负相关。最后，我们发现尽管分解收敛缓慢，但基于POD的低维模型仍会再现实验观察到的尾流偏差的动态变化，以及模拟中确定的全局模式的主要特征。