Image Analysis and Control for Unsteady Structure of Necklace Vortices

研究的目的是通过流动显示技术和图像分析方法，弄清安装在平板上的长柱体或矩形平板周围交汇处流场中产生的项链旋涡的结构，并了解雷诺数和边界层厚度对项链旋涡结构的影响。在对有效长圆柱体周围的项链旋涡进行可视化的情况下，基于圆柱体直径的雷诺数在300~2300范围内变化，圆柱体安装在距平板阅读边三个不同的位置，以较大地改变边界层厚度。结果表明，在雷诺数约为500时，项链涡系的形态发生了变化，使得层流从一个涡系变为三个涡系。当雷诺数为ABOU…时，项链涡型由三涡系变为五涡系在2000年以上，在这个雷诺数中，涡流似乎变得不稳定。根据本实验预测，非定常现象是由五链涡系的原始振动或平壁上层流边界层的过渡引起的非定常流动引起的。此外，还利用风洞试验研究了项链涡对圆柱绕流的影响。结果表明，在连接区，项链旋涡使圆柱体上的分离线后移，使圆柱体后底压增大，阻力减小；为了更清楚地了解项链旋涡的结构细节，尝试增大项链旋涡与挂体尺寸的相对比例。因此，将具有不同纵横比的矩形板作为物体而不是圆柱体。结果表明，长径比w/h分别为0.5、1、2、3、5和7。实验结果表明，项链涡型强烈依赖于长径比，但与雷诺数几乎无关，相同长径比长方板的项链涡流的相对大小和结构取决于长径比相同的长方板的高度和厚度之比。较少

The aims of present investigation are to clarify the structure of necklace vortices produced in the junction flow fields around a long cylinder or a rectangular plate mounted on the flat wall, and to know the effects of the Reynolds number and the boundary layer thickness on the necklace vortices structure by means of the flow visualization techniques and the Image analysis method.In the case of the visualization of necklace vortices around the effectively long cylinder, the Reynolds number based on the cylinder diameter was varied in the range between 300 and 2300, and the cylinder was mounted in three different positions from the reading edge of flat plate to vary widely the boundary layer thickness. As the results, the pattern of the necklace vortex system changes keeping laminar flow from one vortex system to three vortex system at the Reynolds number of about 500. Then the necklace vortex pattern changes from three vortex system to five vortex system at the Reynolds number of abou … More t 2000, in this Reynolds number the vortex flow seemed to become unsteady. It will be predicted from the present experiment that the unsteady phenomena was brought from the original vibration of the five necklace vortex system or from the unsteady flow by the transition of laminar boundary layer on the flat wall. In addition, the effect of the necklace vortex on the flow around a circular cylinder was investigated by using the wind tunnel testing. It was known from the results that in the juncture region the necklace vortex made the separation line on the cylinder move back, and made the base pressure behind the cylinder increase and made the drag decrease.In order to clarify the detail of necklace vortices structure, it was tried to increase the relative scale of necklace vortices to the mounted body size. Therefore, the rectangular plate which have various aspect ratios w/h was picked up as the object body instead of a cylinder. The aspect ratio, which was considered to indicates the various shape of the mounted body, of rectangular plate was varied to w/h=0.5, 1, 2, 3, 5 and 7. As the results, it was known that the necklace vortex pattern was strongly dependent on the aspect ratio of plate, but almost independent apart from Reynolds number in this experiment, and the relative scale and the structure of necklace vortices as to the rectangular plate with the same aspect ratio was decided by the ratio of the plate height to the boundary layer thickness. Less