Bubbles and drops in the vicinity of turbulent/non-turbulent interface in turbulent boundary layers
Bubbles and drops in the vicinity of turbulent/non-turbulent interface in turbulent boundary layers
复制标题
湍流边界层中湍流/非湍流界面附近的气泡和液滴
DOI：
10.1007/s00348-020-03073-8
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发表时间：
2020-10
影响因子：
2.4
通讯作者：
Pan Chong
中科院分区：
文献类型：
--
作者：
Wu Di;Wang Jinjun;Pan Chong
本文首次用二维时间分辨粒子图像测速技术对湍流边界层中湍流/非湍流（T/NT）界面附近湍流区的低涡量泡（气泡）和位流区的高涡量泡（液滴）的特性进行了实验研究。T/NT界面的检测与湍流动能（TKE）标准。气泡和液滴增大了T/NT界面面积，促进了夹带过程。详细的研究表明，气泡上方的T/NT界面通常高于平均界面位置，而液滴下方的T/NT界面则较低。由于气泡和液滴的大小不同，虽然气泡的时间概率远大于液滴，但空间概率相似。此外，首次得到了气泡和液滴的条件平均速度分布和对流速度，特别是在实验中。不同雷诺数下气泡中流体的流向速度均大于周围湍流，而液滴中流体的流向速度小于周围自由流。条件平均流向速度差可以很好地与相应的摩擦速度成比例。此外，气泡和液滴会随着周围流体的速度向下游对流。图形摘要
AbstractThe properties of low-vorticity pockets within the turbulent region (named as bubbles) and high-vorticity pockets within the potential flow region (named as drops) in the vicinity of turbulent/non-turbulent (T/NT) interface in turbulent boundary layers are first experimentally investigated using two-dimensional time-resolved particle image velocimetry. The T/NT interface is detected with a turbulent kinetic energy (TKE) criterion. The bubbles and drops which enlarge the T/NT interface area will promote the entrainment process. A detailed study revealed that the T/NT interface above bubbles is generally higher than the mean interface position, whereas the T/NT interface below drops is lower. Due to different sizes of bubbles and drops, though the temporal probability of bubbles is much larger than drops, the spatial probability is similar. Moreover, the conditional mean velocity distribution and the convection speed of the bubbles and drops are first obtained, especially in experiments. The streamwise velocity of fluids in bubbles at different Reynolds number is larger than surrounding turbulent flow, while in drops, the streamwise velocity is smaller than surrounding free-stream. The conditional mean streamwise velocity difference can be well scaled with respective friction velocity. Besides, bubbles and drops will convect downstream with the velocity of surrounding fluids.Graphic abstract
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