This paper presents an investigation of flow asymmetry around a slender body at high angles of attack. The paper investigated the numerical aspect of simulating such flows. The impact of three simulation parameters, including grid resolution, discretization scheme, and turbulent flow modeling, was assessed. It was shown that insufficient grid density resulted in highly dissipated solution. At high angles, where flow asymmetry is expected to develop around the body, the dissipation from poor grid resolution prevented the flow asymmetry. At higher grid resolution, the solution demonstrated a switch between two bistable states. Two spatial discretization schemes, namely central and bounded, were tested in the course of this study. The results illustrated the necessity to use non-dissipative unbiased discretization schemes. Large eddy simulation was performed using two sub-grid-scale models in addition to a run without a model. The sub-grid-scale models generated similar results except for switching of asymmetry direction and the axial location of separation foci. The study shows that grid resolution and solution scheme have a profound effect on the validity of the simulation of flow around slender bodies at high angles of attack. The study also showed that stringent grid requirements marginalized the effect of the sub-grid-scale model. Computations were then carried out at seven angles of attack $$\alpha = 30^{\circ }$$ , $$40^\circ $$ , $$50^\circ $$ , $$52.5^\circ $$ , $$55^\circ $$ , $$57.5^\circ $$ , and $$60^\circ $$ . Analysis was performed on mean and unsteady flow fields. The total normal force increased with increasing angle of attack. On the other hand, the total side force started to increase rapidly for angles of attack $$\alpha > 50^{\circ }$$ and reached a maximum at $$\alpha =57.5^{\circ }$$ before decreasing at $$\alpha =60^{\circ }$$ . A bistable mode was observed for $$\alpha > 50^{\circ }$$ in which the orientation of resultant forces switches with angle of attack. Comparison of computed dominant frequencies with experiment showed an acceptable agreement. Several dominant modes were identified: very low-frequency mode, low-frequency mode, intermediate-frequency mode, and high-frequency mode. The modes were shown to develop with increasing angle of attack. Surface flow pathlines revealed the existence of separation foci at $$\alpha =57.5^{\circ }$$ and $$60^{\circ }$$ , and a high-frequency tonal mode was observed to accompany the formation of separation foci.

中文翻译：

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研究在高迎角下通过细长体的不对称流动

本文介绍了在大迎角下细长体周围的流动不对称性的研究。该论文研究了模拟此类流动的数值方面。评估了三个模拟参数的影响，包括网格分辨率、离散化方案和湍流建模。结果表明，网格密度不足会导致溶液高度耗散。在高角度，预计流不对称会在身体周围发展，网格分辨率差的耗散阻止了流不对称。在更高的网格分辨率下，该解决方案展示了两个双稳态之间的切换。在本研究过程中测试了两种空间离散化方案，即中心和有界。结果说明了使用非耗散无偏离散化方案的必要性。除了没有模型的运行之外，还使用两个子网格尺度模型进行了大涡模拟。除了不对称方向的切换和分离焦点的轴向位置之外，亚网格尺度模型产生了类似的结果。研究表明，网格分辨率和求解方案对大迎角细长体周围流动模拟的有效性具有深远的影响。该研究还表明，严格的网格要求边缘化了亚网格尺度模型的效果。然后在七个攻角 $$\alpha = 30^{\circ }$$ , $$40^\circ $$ , $$50^\circ $$ , $$52.5^\circ $$ , $55 下进行计算^\circ $$ 、 $$57.5^\circ $$ 和 $$60^\circ $$ 。对平均和非定常流场进行了分析。总法向力随着迎角的增加而增加。另一方面，当攻角 $$\alpha > 50^{\circ }$$ 时，总侧向力开始迅速增加，并在 $$\alpha =57.5^{\circ }$$ 处达到最大值，然后在 $$\alpha 处减小=60^{\circ }$$ 。对于 $$\alpha > 50^{\circ }$$ 观察到双稳态模式，其中合力的方向随着攻角而切换。计算出的主导频率与实验的比较显示出可接受的一致性。确定了几种主要模式：极低频模式、低频模式、中频模式和高频模式。这些模式显示出随着迎角的增加而发展。表面流动路径显示在 $$\alpha =57.5^{\circ }$$ 和 $$60^{\circ }$$ 处存在分离焦点，并且观察到高频色调模式伴随分离焦点的形成.