Flow measurements in the wake of an adhering and oscillating droplet using laser-Doppler velocity profile sensor
Flow measurements in the wake of an adhering and oscillating droplet using laser-Doppler velocity profile sensor
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DOI：
10.1007/s00348-021-03148-0
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发表时间：
2021-03-01
影响因子：
2.4
通讯作者：
Janoske, Uwe
中科院分区：
文献类型：
--
作者：
Burgmann, Sebastian;Dues, Michael;Janoske, Uwe
通过（空气）流去除表面上的液滴是相关的，例如，用于清洁过程或防止电子器件的腐蚀或损坏。液滴运动的条件仍然没有完全弄清楚。液滴开始以临界（空气）流速v（crit）向下游移动。对于增加流速，该过程与液滴的强烈振荡有关。这种振荡被认为是液滴运动与液滴周围的流场一起开始的关键机制。我们报告的测量结果，通过激光多普勒速度分布传感器和热线风速仪在尾流的粘附液滴。由于激光多普勒速度分布传感器具有出色的空间和时间分辨率以及测量双向流动的能力，因此可以在液滴尾流中检测到回流区域。因此，可以得出结论，这种回流结构是驱动机制的强大的流动运动的液滴内的通道流动方向在以前的工作中发现。分析流速的频谱，发现流动也是振荡的;频率峰值与轮廓振荡在相同的范围内。基于频率、直径和流速，可以计算Strouhal数。该Strouhal数在所研究的液滴体积范围内几乎是恒定的，并且在0.015和0.03之间。因此，可以假设可能存在最终导致液滴运动的气动弹性自激效应。
The removal of droplets on surfaces by an (air-) flow is relevant, e.g., for cleaning processes or to prevent corrosion or damage of electronic devices. Still the condition for droplet movement is not fully understood. Droplets start to move downstream at a critical (air-) flow velocity v(crit). For increasing flow velocity, this process is related to a strong oscillation of the droplet. This oscillation is supposed to be a key mechanism for the onset of droplet movement in conjunction with the flow field around the droplet. We report on measurements in the wake of the adhering droplet by means of laser-Doppler velocity profile sensor and hot wire anemometry. Thanks to the excellent spatial and temporal resolution of laser-Doppler velocity profile sensor and its capability to measure bidirectional flows, a backflow region can be detected in the wake of the droplet. Therefore, it can be concluded that this backflow structure is the driving mechanism for the strong flow movement inside the droplet against channel flow direction found in previous work. Analyzing the frequency spectra of the flow velocity, it was found that the flow is also oscillating; frequency peaks are in the same range as for the contour oscillation. Based on frequency, diameter and flow velocity, a Strouhal number can be calculated. This Strouhal number is almost constant in the investigated regime of droplet volumes and is between 0.015 and 0.03. Therefore, it can be assumed that an aeroelastic self-excitation effect may be present that eventually leads to droplet movement.