Reduction of skin friction by microbubbles and its relation with near-wall bubble concentration in a channel
Reduction of skin friction by microbubbles and its relation with near-wall bubble concentration in a channel
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DOI：
10.1007/bf02390723
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发表时间：
1996-12
影响因子：
2.6
通讯作者：
M. M. Guin-M.;H. Kato;H. Yamaguchi;M. Maeda;M. Miyanaga
中科院分区：
文献类型：
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作者：
M. M. Guin-M.;H. Kato;H. Yamaguchi;M. Maeda;M. Miyanaga
壁面附近的流动结构的确定是必不可少的一个清楚的洞察现象的表面摩擦减少微气泡在湍流边界层。一个重要的参数，是在减阻条件下的壁区域中的气泡浓度或空隙率。本文的目的是显示由于在水通道中的微气泡的减阻效果，更重要的是，显示的减阻值对近壁空泡分数的依赖性。为此，专门建造了一个纵横比为10的二维通道，并提供了通过多孔板注入空气的条件。皮肤摩擦力直接测量的微型浮动元件传感器与5毫米的圆形传感盘安装在顶壁齐平67通道高度下游的注射器。在相同的体积速度下，与没有空气的情况相比，气泡存在下的壁面摩擦力减小。详细的空隙率分布在整个通道获得了一个采样探头和光纤探头。更好的崩溃的减阻数据，独立于不同的轮廓形状，被发现时，绘制对近壁空泡分数比对横截面平均空泡分数。虽然这种依赖性再次证实了这种现象基本上是内部区域依赖性的，但远离壁的气泡分布模式的影响的缺乏意味着外部区域的影响的缺乏。
Determination of the flow structure near the wall is essential for a clear insight into the phenomenon of skin friction reduction by microbubbles in a turbulent boundary layer. An important parameter, is the bubble concentration or void fraction in the wall region in drag-reducing conditions. The purpose of this paper is to show drag-reducing effects due to microbubbles in a water channel and, more importantly, to show the dependence of the drag-reduction values on the near-wall void fraction. A two-dimensional channel with an aspect ratio of 10 was specially built for this purpose with provisions for air injection through porous plates. Skin friction was directly measured by a miniature floating element transducer with a 5-mm circular sensing disk mounted flush on the top wall 67 channel-heights downstream of the injector. The wall friction in the presence of air bubbles was found to be reduced under the same bulk velocity when compared with the value without air. Detailed void fraction profiles across the channel were obtained by a sampling probe and a fiber-optic probe. Better collapse of the drag reduction data, independent of different profile shapes, was found when plotted against the near-wall void fraction than against a cross-sectional mean void fraction. While this dependence reconfirms that the phenomena are essentially inner-region dependent, the lack of influence of the bubble distribution patterns away from the wall implies lack of outer region influence.