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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的内部混合机理，对壁面粗糙单元中的三维湍流边界层流动的发展过程进行了测量。在雷诺数为3300时，考察了粗糙度高度与边界层厚度之比为0.135时缝隙尺寸的影响。缝隙产生的变形大小随缝隙宽度的不同而不同，平均速度分布的中心线下移趋势与缝隙宽度无关。平均流动量和湍流量最大值出现在距缝隙下游约四个缝隙处。在适当的速度和长度尺度下，分析了缝隙尺寸对主要流动特性的影响。根据y^+=25时水平面上的偏心特征，目前的流场可分为两个区域：外层区域和内部混合区。此外，内部混合区可以分为四个小群：中心区、相互作用区、弱相互作用区和混合区。VITA分析确定的条件平均花样和高阶矩受缝隙宽度的影响较大。特别是在x/G=0时，空隙宽度对加速和减速事件的峰值比、平均事件频度和平均连续时间的影响与x/G=4时完全相反。在y/δ*0.14为边界时，高阶矩呈现相反的趋势。