This work is concerned with the investigation of fluid-mechanical behaviour and the performance of different subgrid-scale models for LES in the numerical prediction of a confined axisymmetrical bluff-body flow. Four subgrid-scale turbulence models comprising the Smagorinsky model, Dynamic Smagorinsky model, WALE model and subgrid turbulent kinetic energy model, are validated and compared directly against the experimental data. Two different mesh counts are used for the LES studies, one with a higher mesh resolution in the shear layer than the other. It is found that increasing the mesh resolution improves the time-averaged fluctuating velocity profiles, but has less effect on the time-averaged filtered velocity profiles. A comparison against experiment shows that the recirculation zone length is well predicted using LES. The accuracy of the four different subgrid scale models is then assessed by comparing the LES results using the dense mesh with the experiment. Comparisons with the time-averaged axial and radial velocity profiles demonstrate that LES displays good agreement with the experimental data, with the essential flow features captured both qualitative and quantitatively. The subgrid velocity also matches well with the experimental results, but a slight underprediction of the inner shear layer is observed for all subgrid models. In general, it is found that the Smagorinsky and WALE models are more dissipative than the Dynamic Smagorinsky model and subgrid TKE model. Comparison of the spectra against the experiment shows that LES can capture dominant features of the turbulent flow with reasonable accuracy, and weak spectral peaks related to the Kevin-Helmholtz instability and helical vortex shedding are present.

中文翻译：

---

LES 亚网格尺度模型的评估和轴对称钝体流的流体动力学行为研究

这项工作涉及流体力学行为的研究以及 LES 不同亚网格尺度模型在受限轴对称钝体流的数值预测中的性能。包括 Smagorinsky 模型、Dynamic Smagorinsky 模型、WALE 模型和子网格湍流动能模型的四个亚网格尺度湍流模型被验证并直接与实验数据进行比较。LES 研究使用了两种不同的网格数，一种在剪切层中具有比另一种更高的网格分辨率。结果表明，增加网格分辨率可以改善时均脉动速度剖面，但对时均滤波速度剖面的影响较小。与实验的比较表明，使用 LES 可以很好地预测再循环区长度。然后通过将使用密集网格的 LES 结果与实验进行比较来评估四种不同子网格比例模型的准确性。与时间平均轴向和径向速度剖面的比较表明，LES 与实验数据显示出良好的一致性，同时定性和定量地捕获了基本流动特征。亚网格速度也与实验结果很好地匹配，但是对于所有亚网格模型都观察到内部剪切层的轻微预测不足。总的来说，发现Smagorinsky和WALE模型比Dynamic Smagorinsky模型和子网格TKE模型更耗散。光谱与实验的比较表明 LES 可以以合理的精度捕获湍流的主要特征，