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利用PIV(粒子图像测速)测得的不同雷诺数下空腔中垂面的流场序列,分析来流条件对空腔流场涡旋结构及掺混特性的影响。时均流场中存在两个不同大小、旋转方向相反的涡旋。随着雷诺数增大,大涡旋发展壮大并最终受制于固壁边界,小涡旋受大涡旋压迫而减小,两者最终稳定的雷诺数都接近2000,大小涡旋稳定半径分别为0.83D、0.13D(空腔深度)。雷诺数的增大导致来流剪切层与空腔冲撞区域从空腔下游角点延伸至凹腔内部,其中,掺混程度相对较小的区域,面积随雷诺数增加而快速增大;掺混程度相对剧烈的区域,范围会较快趋于稳定。剪切层与空腔下游边壁的冲撞作用,决定了空腔的掺混特性,并使得雷诺应力高值区与时均大涡旋间的形态存在较好的相关性。
The effects of flow conditions on the vortex structure and mixing characteristics of cavity flow field were analyzed using PIV (Particle Image Velocimetry) flow field sequences with different Reynolds numbers. There are two vortexes of different sizes and directions of rotation in the time-averaged flow field. As the Reynolds number increases, the large vortex develops and grows, and eventually is controlled by the solid wall boundary. The small vortex is reduced by the large vortex compression. The final stable Reynolds numbers of both are close to 2000. The stable vortices of the large and small vortex are 0.83D, 0.13D (cavity depth). The increase of Reynolds number leads to the collision zone between the shear layer and the cavity extending from the downstream corner of the cavity to the interior of the cavity. The area with relatively small degree of blending rapidly increases with the increase of Reynolds number. Mix the degree of relatively intense area, the range will tend to stabilize faster. The collision between the shear layer and the downstream wall of the cavity determines the mixing characteristics of the cavity, and the correlation between the Reynolds stress high-value region and the hourly average large vortex has a good correlation.