This paper presents the effects of aspect ratio (B/D, width to height ratio), Reynolds number (Re, based on free incoming flow U_∞ and D), and vortex-induced vibration (VIV) on the pressure properties of elongated hexagonal cylinders through proper orthogonal decomposition (POD) analysis. The examined cases cover B/D = 4, 7, and 10, Re = [3.5 × 10⁴, 4.2 × 10⁵], and primary and secondary VIV resonances. The experimental results show that the mean pressure field is insensitive to Re and VIV, while the fluctuating pressure significantly depends on B/D, Re, and VIV. For the cylinder in fixed state, the fluctuating pressure field can be decomposed into three typical fluctuating modes, i.e., leading-edge fluctuating mode (LEFM), trailing-edge fluctuating mode (TEFM), and their coupling fluctuating mode (CFM). With an increase in B/D, the TEFM and CFM obviously decay, while the LEFM slightly intensifies. On the other hand, with an increase in Re, the TEFM obviously enhances, while the LEFM generally weakens. The above observations suggest that the effects of cylinder leading-edge vortices on trailing-edge vortices gradually reduce with increasing B/D and Re. For the cylinder in VIV state, the fluctuating pressure field can be decomposed into four typical fluctuating modes, i.e., LEFM, CFM, distorted TEFM, and motion-induced fluctuating mode (MIFM). Compared to the above fixed case, the two emerging modes, i.e., distorted TEFM and MIFM, are the underlying mechanisms of VIV. But in primary and secondary VIV resonances, the distorted TEFM and MIFM capture different energy percentages, which is the underlying physic of the cylinder multi-lock-in phenomenon.

本文介绍了长径比（B/D ，宽高比）、雷诺数（Re，基于自由流入流U _∞和D ）和涡激振动 (VIV) 对细长六边形压力特性的影响通过适当的正交分解 (POD) 分析来分析气缸。检查的案例涵盖B/D  = 4、7 和 10、Re = [3.5 × 10 ⁴ , 4.2 × 10 ⁵ ] 以及初级和次级 VIV 共振。实验结果表明，平均压力场对Re和VIV不敏感，而脉动压力则显着依赖于B/D、Re和VIV。对于固定状态的气缸，脉动压力场可分解为三种典型的脉动模态，即前沿脉动模态（LEFM）、后缘脉动模态（TEFM）及其耦合脉动模态（CFM）。随着B/D的增加，TEFM和CFM明显衰减，而LEFM略有增强。另一方面，随着Re的增加，TEFM明显增强，而LEFM普遍减弱。上述观察结果表明，随着B/D和Re的增加，圆柱体前缘涡对后缘涡的影响逐渐减小。对于处于VIV状态的气缸，脉动压力场可分解为四种典型脉动模态，即LEFM、CFM、扭曲TEFM和运动诱发脉动模态(MIFM)。与上述固定情况相比，扭曲的TEFM和MIFM这两种新兴模式是VIV的底层机制。但在初级和次级 VIV 共振中，扭曲的 TEFM 和 MIFM 捕获不同的能量百分比，这是圆柱体多重锁定现象的基础物理原理。