基于PIV技术分析颗粒在湍流边界层中的行为

采用粒子图像测速技术(particle image velocimetry, PIV)在平板湍流边界层内开展实验研究,对比颗粒相及单相液体的平均速度剖面、湍流强度、雷诺应力等湍流统计量,分析颗粒在湍流边界层中的行为.利用空间多尺度局部平均涡量的概念提取壁湍流发卡涡展向涡头(顺向涡)并统计其数量规律,得到不同法向位置处顺向涡周围流向脉动速度及流线的空间拓扑结构,比较分析顺向涡发展程度及周围的湍流相干结构.结果发现:与清水工况相比,颗粒相湍流边界层的缓冲层变薄、对数律区下移,湍流强度得到增强,雷诺应力在对数律区有所增大;颗粒的流向脉动速度在展向涡周围的分布与清水工况不同,颗粒能够被流体展向涡周围的猝发过程有效传递;颗粒相的顺向涡涡核较大,且随着法向位置的升高逐渐发展完整,涡和条带在流向上拉伸得更长;同时发现在两种工况下,顺向涡的左下方始终存在一个逆向涡,颗粒相逆向涡的形成弱于单相流体;两种工况下的顺向涡数量均随着法向位置的升高而减少,最后逐渐趋于稳定.

PIV EXPERIMENTAL INVESTIGATION ON THE BEHAVIOR OF PARTICLES IN THE TURBULENT BOUNDARY LAYER

The particle image velocimetry (PIV) is used to conduct experimental research in the solid-liquid two-phase plane turbulent boundary layer. The turbulence statistics such as the average velocity profile, turbulence intensity and Reynolds stress of the particle phase and single-phase clean water are compared to analyze the behavior of the particles in the turbulent boundary layer. The concept of multi-scale spatial locally-averaged vortices is utilized to extract the spatial topologies of the spanwise vortex head and the statistic of the prograde vortex is acquired. From that, the spatial topologies of the fluctuating velocity and streamlines around the prograde vortex at different normal positions can be obtained. The degree of development of the prograde vortex and the surrounding turbulence coherence structure can be compared and analyzed. The results show that compared with the clean water conditions, the buffer layer of the turbulent boundary layer of the particle phase becomes thinner, the logarithmic region moves downward, the turbulence intensity is enhanced, and the Reynolds stress in the logarithmic law region is increased. The fluctuating velocity of the particle phase is different from the clear water condition around the vortex, and the particles can be effectively transferred by the burst process around the spanwise vortex. The particle-laden flow has a large prograde vortex core and develops as the normal position rises. The vortex and the band stretch longer in the flow direction. At the same time, it is found that there is always a retrograde vortex in the lower left of the prograde vortex under both conditions, and the formation of retrograde vortex in the particle-laden flow is weaker than that of single-phase fluids. The number of prograde vortices in both conditions decreases with the increase of the normal position, and finally gradually stabilizes.