Blaauw Luuk J, Lohse Detlef, Huisman Sander G
Physics of Fluids Group and Max Planck Center for Complex Fluid Dynamics, Department of Science and Technology, and J.M. Burgers Center for Fluid Dynamics, University of Twente, Enschede, The Netherlands.
Max Planck Institute for Dynamics and Self-Organization, Am Faßberg 17, Göttingen, Germany.
Philos Trans A Math Phys Eng Sci. 2023 Mar 20;381(2243):20220127. doi: 10.1098/rsta.2022.0127. Epub 2023 Jan 30.
Using the Taylor-Couette geometry we experimentally investigate the effect of salt on drag reduction caused by bubbles present in the flow. We combine torque measurements with optical high-speed imaging to relate the bubble size to the drag experienced by the flow. Previous studies have shown that a small percentage of air (4%) can lead to dramatic drag reduction (40%). In contrast to previous laboratory experiments, which mainly used fresh water, we will vary the salinity from that of fresh water to the average salinity of ocean water. We find that the drag reduction is increasingly more inhibited for increasing salt concentrations, going from 40% for fresh water to just 15% for sea water. Salts present in the working fluid inhibit coalescence events, resulting in smaller bubbles in the flow and, with that, a decrease in the drag reduction. Above a critical salinity, increasing the salinity has no further effect on the size of bubbles in the flow and thus the drag experienced by the flow. Our new findings demonstrate the importance of sodium chloride on the bubbly drag reduction mechanism, and will further challenge naval architects to implement promising air lubrication systems on marine vessels. This article is part of the theme issue 'Taylor-Couette and related flows on the centennial of Taylor's seminal paper (part 1)'.
利用泰勒-库埃特装置，我们通过实验研究了盐对流动中气泡引起的减阻效果的影响。我们将扭矩测量与光学高速成像相结合，以关联气泡大小与流动所受的阻力。先前的研究表明，少量空气（4%）就能显著降低阻力（40%）。与之前主要使用淡水的实验室实验不同，我们将盐度从淡水变化到海水的平均盐度。我们发现，随着盐浓度的增加，减阻效果越来越受到抑制，从淡水时的40%降至海水时的仅15%。工作流体中的盐抑制了聚并事件，导致流动中的气泡更小，从而使减阻效果降低。在超过临界盐度后，增加盐度对流动中气泡的大小以及流动所受的阻力不再有进一步影响。我们的新发现证明了氯化钠对气泡减阻机制的重要性，并将进一步促使船舶设计师在船舶上应用有前景的空气润滑系统。本文是主题为“泰勒开创性论文发表百年之际的泰勒-库埃特及相关流动（第1部分）”的一部分。
