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Internal mixing mechanism of a turbulent boundary layr formed by spanwise gaps between roughness element

粗糙度单元间翼展间隙形成的湍流边界层的内部混合机制

基本信息

批准号：
05650164
负责人：
OSAKA Hideo
金额：
$ 1.34万
依托单位：
Department of Engineering, Yamaguchi University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1993
资助国家：
日本
起止时间：
1993 至 1994
项目状态：
已结题

项目摘要

Measurement was made on the 3-D development of a turbulent boundary layr flow through a gap in an isolated wall-mounted roughness element to examine the internal mixing mechanism inwall shear flow. The effect of gap size was examined for a ratio of roughness height to boundary layr thickness 0.135 at a Reynolds number of 3300. The magnitude of distortion produced by the gap varies with gap width.Centerline downstrem tendency of the mean velocity profile is almost similar, independent of gap width. Mean flow and turbulence quantities shows maximum distortion at about four gap with downstream of the gap. The gap size effect on major flow features was also analyzed with both the appropriate velocity and length scales. From the off-centerline features in the horizontal plane at y^+=25, present flow field can be divided into two regions, outer layr region and internal mixing region. An internal mixing region, furthermore, can be divided into four small groups, center region, interacted region, weak interaction region and mixing region. The interaction is more intense for the large gap than for small one.Conditional averaged patterns detemined with the VITA analysis and higher-order moments are significantly affected by the gap width. In particular, the gap width effects on the peak ratio, mean event frequency and mean consecutive time for both accelerating and decelerating event at x/G=0 are completely contrary to those at x/G=4. The higher-order moments show the reverse tendency at y/delta*0.14 as the border.

为了研究壁面剪切流动的内部混合机制，对壁面隔离壁面粗糙度单元间隙内湍流边界层流动的三维发展进行了测量。当雷诺数为3300时，粗糙度高度与边界层厚度之比为0.135，考察了间隙尺寸的影响。由间隙产生的畸变大小随间隙宽度的变化而变化。平均速度剖面的中心线下游趋势几乎相似，与间隙宽度无关。平均流动和湍流量显示，在间隙下游约四个间隙处畸变最大。在适当的速度和长度尺度下，分析了间隙大小对主要流动特征的影响。从y^+=25处水平面的离中心线特征可以将当前流场划分为两个区域，外层区域和内部混合区域。内部混合区可分为中心区、相互作用区、弱相互作用区和混合区四个小区域。大间隙的相互作用比小间隙的相互作用更强烈。用VITA分析和高阶矩确定的条件平均模式受间隙宽度的显著影响。特别是在x/G=0时，间隙宽度对加速和减速事件的峰值比、平均事件频率和平均连续时间的影响与x/G=4时完全相反。高阶矩在y/delta*0.14处显示相反的趋势。