Streamwise oscillations of a cylinder in a steady current. Part 1. Locked-on states of vortex formation and loading
Streamwise oscillations of a cylinder in a steady current. Part 1. Locked-on states of vortex formation and loading
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DOI：
10.1017/s0022112000002214
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发表时间：
2001-01
影响因子：
3.7
通讯作者：
O. Çetiner;D. Rockwell
中科院分区：
文献类型：
--
作者：
O. Çetiner;D. Rockwell
采用高图像密度粒子图像测速技术结合瞬时力测量，对定常均匀流中圆柱体的流向振荡进行了实验研究。这种方法允许洞察载荷和涡量的模式和流线拓扑结构在近尾流之间的关系。与均匀流中圆柱体横向振荡引起的经典锁定状态类似，由于流向振荡，有可能获得锁定或准锁定状态。然而，在这些情况下，横向力的重复签名不是正弦曲线;相反，它是强烈调制的，相应的光谱可以表现出几个尖锐的峰值。主峰值可以在一个非常宽的范围内变化，从分谐波延伸到气缸振荡频率的第三谐波;对于横向力签名的某些锁定状态，气缸振荡频率处的谱峰实际上被抑制。顺向力的相应瞬时轨迹和光谱简单地显示了气缸振动频率处谱峰的主导地位。载荷的进一步解释提供的横向和线力系数的李萨如模式。所有这些特征都与近尾流中旋涡形成的瞬时模式有关。在一个典型的圆柱体振荡周期中，这些模式可以分为两大类：卡门式脱落和几乎“冻结”的脱落涡流阵列。在一个振荡周期中，这些基本模式的发生顺序决定了横向力的瞬时特征和时间平均谱。
Streamwise oscillations of a circular cylinder in a steady uniform flow are investigated experimentally using a technique of high-image-density particle image velocimetry, in conjunction with instantaneous force measurements. This approach allows insight into the relationship between the loading and the patterns of vorticity and streamline topology in the near wake. In analogy with the classical locked-on state arising from transverse oscillations of a cylinder in uniform flow, it is possible to attain either locked-on or quasi-locked-on states due to streamwise oscillations. In these cases, however, the repetitive signature of the transverse force is not sinusoidal; rather, it is strongly modulated and the corresponding spectra can exhibit several sharply defined peaks. The predominant peak can vary over a remarkably wide range, extending from the subharmonic to the third harmonic of the cylinder oscillation frequency; for certain locked-on states of the transverse force signature, the spectral peak at the cylinder oscillation frequency is actually suppressed. Corresponding instantaneous traces and spectra of the in-line force simply show dominance of the spectral peak at the cylinder oscillation frequency. Further interpretation of the loading is provided in terms of Lissajous patterns of the transverse and in-line force coefficients. All of these features are related to the instantaneous patterns of vortex formation in the near wake. During a typical cycle of the cylinder oscillation, these patterns can be divided into two broad categories: Kármán-like shedding; and a nearly ‘frozen’ array of shed vortices. The order of occurrence of these basic patterns during an oscillation cycle dictates the instantaneous signatures and time-averaged spectra of the transverse force.