Experimental study of coherent structures in a solid-liquid turbulent boundary layer
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摘要: 液固两相湍流是工业和工程中常见的流动状态，研究颗粒—湍流两相之间的作用规律和湍流调制的机理，对有效调控化工过程传热传质具有重要意义。采用粒子图像测速技术（PIV）对液固两相平板湍流边界层进行实验研究，分析在同一来流速度下加入固相颗粒和清水时水平板湍流边界层的平均速度剖面、湍流强度变化情况。通过空间局部平均速度结构函数和相干结构条件采样技术，提取并对比壁湍流相干结构"喷射"和"扫掠"事件的脉动速度、雷诺切应力以及展向涡量的二维空间拓扑形态。发现，同清水工况相比，湍流边界层缓冲层有变薄的趋势，对数律区内移，湍流强度和雷诺切应力均有所增强。相干结构在猝发时，脉动速度增强，雷诺切应力相对增大，展向涡量的发展受到促进，这表明实验中颗粒的存在使得湍流边界层中流体脉动增强，相干结构"喷射"和"扫掠"的强度相应增大，动量和能量的输运增强。
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关键词:
- 液固两相流 /
- 湍流边界层 /
- 相干结构 /
- PIV /
- 空间局部平均速度结构函数
Abstract: Solid-liquid turbulent flows are common in industrial and engineering processes.Study of the interactions between particles as well as turbulence and turbulence modulation is extremely significant, which can play an guidance role in practical engineering application for heat and/or mass transfer in chemical processes.Coherent structure in the turbulent boundary layer of particle-laden flows is experimentally investigated using Particle Image Velocimetry (PIV). Study of the change of the mean velocity profile and the turbulent intensity in the horizontal turbulent boundary layer of water and with polythene is conducted, which is used as the dispersed phase.Based on the concept of multi-scale spatial locally averaged structure function, conditional sampling and phase average methods are employed to extract and analyze the spatial topologies of the streamwise and normal fluctuating velocities, spanwise vorticity, Reynolds shear stress of the ejection and sweep events.The results show that the buffer layer of the turbulent boundary layer has thinning tendency and logarithmic layer down-shift, the turbulence intensity and the Reynolds stress are also enhanced due to the existence of particles.The amplitude of longitudinal and vertical fluctuating velocity components, as well as that of the spanwise vorticity and Reynolds shear stress can be manipulated obviously both in ejection and sweeping events, all parameters were increased. It imply that the turbulence intensity in the near-wall region in the two burst events increase, and the momentum and energy transport strengthen for the exist of particle in the experiment. -
图 3 湍流度以及雷诺切应力沿法向位置y+的分布
Figure 3. Turbulent intensity and Reynolds shear stress distributions in the wall-normal direction
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