Bubbly drag reduction investigated by time-resolved ultrasonic pulse echography for liquid films creeping inside a turbulent boundary layer
Bubbly drag reduction investigated by time-resolved ultrasonic pulse echography for liquid films creeping inside a turbulent boundary layer
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DOI：
10.1016/j.expthermflusci.2018.12.025
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发表时间：
2019-05
影响因子：
3.2
通讯作者：
H. Park;Y. Tasaka;Y. Murai
中科院分区：
文献类型：
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作者：
H. Park;Y. Tasaka;Y. Murai
通过测量两相湍流边界层内沿壁面沿着蠕动的液膜，研究了气泡润滑的减阻作用。我们开发了一种非侵入性的时间分辨超声脉冲回波成像技术，用于以3 kHz的剖面速率和50 μm的空间分辨率对液体膜进行成像。在100米长的水箱中拖曳的4米长的平底模型船获得了各种膜图案，其中最大空气喷射的减阻率为30%。我们发现，液膜厚度范围从50到150壁单元的单相湍流边界层，这部电影是厚于缓冲层的深度。随着空气注入流量的增加，平均厚度下降接近缓冲层的限制，而偏度和峰度的概率密度函数的膜厚增加。根据峰度检测膜形式的突然转变，允许通过超声脉冲回波描记术监测分散的气泡聚结成大的细长气泡的标准。
Frictional drag reduction due to bubble lubrication was investigated by measuring liquid films creeping along a wall within a two-phase turbulent boundary layer. We developed noninvasive time-resolved ultrasonic pulse echography for imaging a liquid film at a profiling rate of 3 kHz and a spatial resolution of 50 μm. Various film patterns were obtained for a 4-m-long flat-bottom model ship towed in a 100-m-long water tank, where a drag reduction rate of 30% was recorded for maximum air injection. We found that the liquid-film thickness ranged from 50 to 150 wall units of the single-phase turbulent boundary layer; this film was thicker than the buffer layer depth. With an increase in the air injection flow rate, the average thickness decreased close to the buffer layer limit while the skewness and kurtosis of the probability density function of the film thickness increased. A sudden transition of the film form was detected according to the kurtosis, allowing the monitoring of the criteria of the coalescence of dispersed bubbles into large elongated bubbles via ultrasonic pulse echography.