The behaviour of circular synthetic jets in a laminar boundary layer
The behaviour of circular synthetic jets in a laminar boundary layer
复制标题
层流边界层中圆形合成射流的行为
作者：
S. Zhong;F. Millet;N. Wood
本文在作动器工作条件和自由速度分别为0.05和0.1ms-1的范围内，对平板层流边界层中圆形合成射流进行了染料流动显示。这项工作的目的是研究合成射流与边界层的相互作用以及由于这种相互作用而产生的旋涡结构的性质。研究了雷诺数（Re）、速度比（VR）和Strouhal数（St）对合成射流特性的影响。在低Re和VR下，合成射流产生的涡结构表现为高度拉伸的发夹涡。在中等Re和VR下，这些结构卷起形成涡环，当它们进入边界层时，涡环经历相当大的倾斜和拉伸。这些涡环最终将传播到边界层外，因此合成射流对近壁流动的影响将被限制在射流出口的近场。在高Re和VR下，涡环似乎经历了一定程度的倾斜，但没有明显的拉伸。它们迅速穿透边界层的边缘，对近壁流动产生非常有限的影响。因此，人们认为，在低Re和VR下产生的发夹涡可能是有效控制流动分离的理想结构。本文还提出了一个涡模型来解释涡倾斜的机理。
Abstract Dye flow visualisation of circular synthetic jets was carried out in laminar boundary layers developing over a flat plate at a range of actuator operating conditions and freestream velocities of 0·05 and 0·1ms–1. The purpose of this work was to study the interaction of synthetic jets with the boundary layer and the nature of vortical structures produced as a result of this interaction. The effects of Reynolds number (Re), velocity ratio (VR ) and Strouhal number (St) on the behaviour of synthetic jets were studied. At low Re and VR , the vortical structures produced by synthetic jets appear as highly stretched hairpin vortices attached to the wall. At intermediate Re and VR , these structures roll up into vortex rings which experience a considerable amount of tilting and stretching as they enter the boundary layer. These vortex rings will eventually propagate outside the boundary layer hence the influence of the synthetic jets on the near wall flow will be confined in the near field of the jet exit. At high Re and VR , the vortex rings appear to experience a certain amount of tilting but no obvious stretching. They penetrate the edge of the boundary layer quickly, producing very limited impact on the near wall flow. Hence it is believed that the hairpin vortices produced at low Re and VR are likely to be the desirable structures for effective flow separation control. In this paper, a vortex model was also described to explain the mechanism of vortex tilting.