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Sensitivity analysis of hybrid methods for the flow around the Ahmed body with application to passive control with rounded edges
Computers & Fluids ( IF 2.8 ) Pub Date : 2021-01-01 , DOI: 10.1016/j.compfluid.2020.104757
Francois Delassaux , Iraj Mortazavi , Emmanuelle Itam , Vincent Herbert , Charles Ribes

Abstract A comparative study of SST RANS and three hybrid approaches (SAS, DDES and SBES methods) is performed to analyse the flow around the 25∘ Ahmed body. The DDES approach is then selected as the reference model, based on comparison of numerical results. The main study is based on grid and time step influence over the simulation results. All results are compared to in-house experiments. The three grids 15l, 20l and 30l (related to the number of prism layers in the boundary layer) show a fair prediction for both drag Cd and lift Cl coefficients. The best prediction is obtained with the 30l grid with an accurate prediction of Cd and Cl values as well as the main flow characteristics, compared to experiments. Another part of this paper focuses on the time step effect on the computational accuracy. Then, the flow around various rounded edge Ahmed body configurations is compared to experiments in order to validate the robustness of the numerical methodology. The rounded edge flow topologies are therefore deeply investigated. It is shown that they act as passive flow control and significantly influence the flow topology and aerodynamical coefficients. In fact, the rounded strategy modifies the flow detachment and weakens the onset of C-pillar vortices, which directly reduce drag and lift coefficients.

中文翻译:

Ahmed 体周围流动的混合方法的灵敏度分析,并应用于带圆形边缘的被动控制

摘要 对 SST RANS 和三种混合方法(SAS、DDES 和 SBES 方法)进行了比较研究,以分析 25∘ Ahmed 体周围的流动。然后根据数值结果的比较,选择 DDES 方法作为参考模型。主要研究基于网格和时间步长对模拟结果的影响。所有结果都与内部实验进行了比较。三个网格 15l、20l 和 30l(与边界层中棱柱层的数量有关)显示了对阻力 Cd 和升力 Cl 系数的合理预测。最好的预测是使用 30l 网格获得的,与实验相比,它可以准确预测 Cd 和 Cl 值以及主要流动特性。本文的另一部分侧重于时间步长对计算精度的影响。然后,将围绕各种圆形边缘 Ahmed 体配置的流动与实验进行比较,以验证数值方法的稳健性。因此,对圆边流拓扑进行了深入研究。结果表明,它们充当被动流动控制并显着影响流动拓扑和空气动力学系数。事实上,圆形策略改变了流动分离并减弱了 C 柱涡流的出现,这直接降低了阻力和升力系数。
更新日期:2021-01-01
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