Unsteady RANS (URANS), hybrid LES/RANS and IDDES simulations were conducted to numerically investigate the velocity field around, and pressures distribution and forces over a square cylinder immersed in a uniform, steady oncoming flow with Reynolds number Re = 21,400. The vortex shedding responses in terms of Strouhal number, the pressure distribution, the velocity profile and the velocity fluctuations obtained by numerical simulations are compared with experimental data. Compared with 2D URANS simulation, 3D simulations using hybrid LES/RANS and IDDES models provide more accurate prediction on the responses in the wake, including mean streamwise velocity profile and rms velocity fluctuations. This also results in more accurate prediction of time-averaged surface pressure coefficient on the rear surface obtained by 3D hybrid LES/RANS and IDDES simulations than by URANS simulation. When a hybrid LES/RANS model or IDDES model is used, a more accurate prediction for either pressure coefficient or velocity profile (especially in the far wake region) is not guaranteed by increasing the mesh resolution along the spanwise direction of the square cylinder.

中文翻译：

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RANS和混合LES / RANS模拟方筒上的流动

进行了非稳态RANS（URANS），混合LES / RANS和IDDES仿真，以数值方式研究了浸入在雷诺数Re = 21,400的均匀，稳定的迎面流中的方筒周围的速度场以及压力分布和作用力。将通过数值模拟获得的涡流脱落响应，斯特劳哈尔数，压力分布，速度分布和速度波动与实验数据进行了比较。与2D URANS仿真相比，使用混合LES / RANS和IDDES模型的3D仿真可提供关于尾随响应的更准确的预测，包括平均水流速度分布和均方根速度波动。与URANS模拟相比，通过3D混合LES / RANS和IDDES模拟获得的后表面时间平均表面压力系数预测也更准确。当使用混合LES / RANS模型或IDDES模型时，不能通过增加沿方形圆柱体的展向方向的网格分辨率来确保对压力系数或速度分布图（尤其是在远尾流区域）进行更准确的预测。