Effect of near-wake jet on the lock-in of a freely vibrating square cylinder
Effect of near-wake jet on the lock-in of a freely vibrating square cylinder
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DOI：
10.1063/1.5085272
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发表时间：
2019-05
影响因子：
4.6
通讯作者：
K. Narendran;R. Jaiman
中科院分区：
文献类型：
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作者：
K. Narendran;R. Jaiman
本文对自由振动的方柱体底部稳定放气问题进行了数值研究。特别是，我们专注于抑制涡激振动（VIV）和减少阻力的弹性安装方柱在层流条件下，通过近尾迹射流。我们研究的基础出血机制，在近尾区的一个方柱和它的影响的流动动力学和尾流特性的固定（非锁定）和自由振动（锁定）的条件。我们认为近尾流射流参数作为泄放系数（Cq）的函数，泄放系数（Cq）是近尾流射流速度与自由速度的比率，并且取决于基于圆柱直径的雷诺数（Re）。层流Re范围内，即Re = 40，60，100和150的水动力系数和流动特性的调查进行。对于所有考虑的雷诺数，在升力系数谱图中观察到一个主频率峰，但对于Re = 150，在Cq = 0.175和0.2处观察到两个峰。更高的Cq值表现得像一个分离板，从而防止交替剪切层的相互作用。平均阻力的变化与圆柱表面周围和沿着流向位置的压力分布有关。这将导致较薄的尾流宽度、较弱的涡流和较高的涡流脱落频率，如文献中先前所观察到的。当Re ∈ [40，150]时，由于近尾流射流的存在，圆柱底侧的压力系数出现了尖峰，这是阻力系数波动的原因。通过详细的定性分析，我们证明了由于近尾流射流在尾流区域形成了多个旋涡。我们观察到反向旋转对的再循环流体侧翼在近尾流射流的位置，并检查由于射流的基础压力的恢复。我们证明了大循环流体气泡分裂成许多较小的反向旋转的流体，由于高速射流，导致在尾流区的流动剖面的稳定。我们扩展这项调查，以量化的影响，近尾流射流上的两个自由度的缸系统在代表性的雷诺数Re = 100和三个质量比m* = 1，2和3。我们证明了减少90%的峰值横向涡激振幅相比，平缸counter.We提出了一个自由振动的方柱的数值研究与稳定的出血在其基础侧。特别是，我们专注于抑制涡激振动（VIV）和减少阻力的弹性安装方柱在层流条件下，通过近尾迹射流。我们研究的基础出血机制，在近尾区的一个方柱和它的影响的流动动力学和尾流特性的固定（非锁定）和自由振动（锁定）的条件。我们认为近尾流射流参数作为泄放系数（Cq）的函数，泄放系数（Cq）是近尾流射流速度与自由速度的比率，并且取决于基于圆柱直径的雷诺数（Re）。层流Re范围内，即Re = 40，60，100和150的水动力系数和流动特性的调查进行。在升力系数谱图中观察到一个单一的主频率峰的所有R…
We present a numerical study of a freely vibrating square cylinder with steady bleeding at its base side. In particular, we focus on the suppression of vortex-induced vibration (VIV) and the reduction of drag force for the elastically mounted square cylinder at a laminar flow condition via near-wake jet. We examine the base bleeding mechanism in the near-wake region of a square cylinder and its influence over the flow dynamics and the wake characteristics for both stationary (nonlock-in) and freely vibrating (lock-in) conditions. We consider the near-wake jet parameter as a function of the bleed coefficient (Cq), which is the ratio of near-wake jet flow velocity to the freestream velocity and depends on the Reynolds number (Re) based on the diameter of the cylinder. Investigations of the hydrodynamic coefficients and the flow features are carried out for the laminar Re range, namely, Re = 40, 60, 100, and 150. A single dominant frequency peak is observed in the lift coefficient spectrum plot for all the Reynolds numbers considered, but two peaks are observed for Re = 150 at Cq = 0.175 and 0.2. Higher Cq values behave like a splitter plate thereby preventing the interaction of alternating shear layers. The variation of the mean drag is associated with the pressure distribution around the cylinder surface and along the streamwise locations. This leads to a thinner wake width, weaker vortices, and higher vortex shedding frequency as observed earlier in the literature. The sharp spikes of pressure coefficient at the base side of the cylinder are observed for Re ∈ [40, 150] due to the near-wake jet, accounting for the fluctuations of drag force coefficient. We demonstrate the formation of multiple vortices at the wake region due to the near-wake jet from our detailed qualitative analysis. We observe counter-rotating pair of recirculating fluids flanking at the near-wake jet location and examine the recovery of base pressure due to the jet flow. We demonstrate the splitting of big circulation fluid bubble into many smaller counter-rotating fluids due to high-velocity jet flow, resulting into the stabilization of flow profiles in the wake region. We extend this investigation to quantify the effect of the near-wake jet on the two-degree-of-freedom cylinder system at the representative Reynolds number Re = 100 and three mass ratios m* = 1, 2, and 3. We demonstrate the reduction of peak transverse VIV amplitude by 90% in comparison to the plain cylinder counterpart.We present a numerical study of a freely vibrating square cylinder with steady bleeding at its base side. In particular, we focus on the suppression of vortex-induced vibration (VIV) and the reduction of drag force for the elastically mounted square cylinder at a laminar flow condition via near-wake jet. We examine the base bleeding mechanism in the near-wake region of a square cylinder and its influence over the flow dynamics and the wake characteristics for both stationary (nonlock-in) and freely vibrating (lock-in) conditions. We consider the near-wake jet parameter as a function of the bleed coefficient (Cq), which is the ratio of near-wake jet flow velocity to the freestream velocity and depends on the Reynolds number (Re) based on the diameter of the cylinder. Investigations of the hydrodynamic coefficients and the flow features are carried out for the laminar Re range, namely, Re = 40, 60, 100, and 150. A single dominant frequency peak is observed in the lift coefficient spectrum plot for all the R...