Abstract Numerical simulations with high grid resolutions are conducted to investigate the flow past a square cylinder at the Reynolds number of 2 . 2 × 1 0 4 and the critical angle of attack of 14 ° . The focus is on the unsteadiness with a much lower frequency than that of von Karman vortex shedding. This study confirms the existence of low-frequency unsteadiness even for the square cylinder. The qualitative and quantitative features of low-frequency unsteadiness are systematically analyzed in terms of forces, vortex shedding and separation bubble. The low frequency with the outstanding peak is much lower than the frequency of von Karman vortex shedding; specifically, it is about 0 . 14 f v K , where f v K is the vortex-shedding frequency. The low-frequency unsteadiness can be “felt” in the time series of forces and in the dynamics of vortex shedding and separation bubble. For both drag and lift, the unsteadiness is manifested by the low-frequency modulation of force amplitude and by the low-frequency periodic variation between the high and low values of the mean drag and lift over a vortex shedding cycle. The smaller force amplitude is accompanied simultaneously by the vortex shedding with longer formation length and weaker spanwise correlation, together with longer separation bubble on the flow-reattachment side of the cylinder.

中文翻译：

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雷诺数为 2.2×104 时临界角为 14° 的方柱体周围流动的低频不稳定性

摘要 进行了高网格分辨率数值模拟，研究了雷诺数为2 时通过方柱体的流动。2×1 0 4 和14°的临界攻角。重点是频率比 von Karman 涡旋脱落频率低得多的不稳定性。这项研究证实了即使是方形圆柱体也存在低频不稳定性。从力、涡旋脱落和分离气泡等方面系统地分析了低频不稳定的定性和定量特征。具有突出峰值的低频远低于von Karman涡旋脱落频率；具体来说，它大约是 0 。14 fv K ，其中 fv K 是涡旋脱落频率。在力的时间序列和涡旋脱落和分离气泡的动力学中可以“感觉到”低频不稳定。对于阻力和升力，不稳定性表现为力振幅的低频调制以及涡旋脱落周期内平均阻力和升力的高低值之间的低频周期性变化。较小的力幅值同时伴随着涡旋脱落，形成长度较长，展向相关性较弱，以及圆柱体流动重附侧的分离气泡较长。不稳定表现为力振幅的低频调制以及涡旋脱落周期内平均阻力和升力的高低值之间的低频周期性变化。较小的力幅值同时伴随着涡旋脱落，形成长度较长，展向相关性较弱，以及圆柱体流动重附侧的分离气泡较长。不稳定表现为力振幅的低频调制以及涡旋脱落周期内平均阻力和升力的高低值之间的低频周期性变化。较小的力幅值同时伴随着涡旋脱落，形成长度较长，展向相关性较弱，以及圆柱体流动重附侧的分离气泡较长。