基于Stereo-PIV技术的三维发卡涡结构定量测量研究

发卡涡是湍流相干结构研究中最为关注的内容,实现发卡涡三维结构的定量测量并进行流体动力学分析,对深入研究湍流相干结构、实现湍流精准控制等具有重要意义.本研究通过对合成射流装置进行合理控制,使得层流边界层中产生了规则的人造发卡涡结构,进而用体视图像粒子测速仪(Stereo-PIV)锁相实验技术对发卡涡结构所在的三维空间流场进行了定量测量,并得到了一个完整周期内形成的发卡涡三维结构的空间流场. 结果发现,重构所得的三维发卡涡结构质量较高, 实验技术和方案具有可行性.发卡涡结构所在空间流场情况,符合目前人们对于发卡涡、高低速条带、喷射和扫掠事件的常规认识. 此外,对近壁二次流向涡、展向涡量集中区域的展向涡头和强剪切区域、与低速喷射流体相关的汇聚流动和发散流动等有了更细致的认识.同时, 也探讨了"基于二维脉动流场的相关特征去重构发卡涡三维流场"的可行性.为进一步定量探究发卡涡结构的形成演化、不同涡结构的融合及二次诱导等壁湍流相干结构问题提供思路. 

EXPERIMENTAL STUDY ON QUANTITATIVE MEASUREMENT OF THREE-DIMENSIONAL STRUCTURE OF HAIRPIN VORTEX BY STEREO-PIV

Hairpin vortex is one of the most concerned paradigm in the study of turbulent coherent structures. The quantitative experimental measurement and hydrodynamic analysis of the three-dimensional hairpin vortex structures~is of great significance for further~applications in the turbulent flow control.~In this study, with an optimized arrangement of the synthetic jet device, a~series of~regular artificial hairpin vortex structures~are~produced in the laminar boundary layer, and then the three-dimensional shapes of~hairpin vortex structures are quantitatively revealed by stereoscopic particle image velocimetry (Stereo-PIV) using phase-locking technique. The three-dimensional flow field of the hairpin vortex within a complete period is obtained. The quality of the reconstructed three-dimensional hairpin vortex structure is reliable. The results are in line with the general knowledge of hairpin vortex, low/high~speed streaks and~ejection/sweeping~events. In addition, we acquire a more detailed understanding of the near-wall secondary vortex, the spanwise~vortex head and the area of strong shear in the spanwise~vorticity~concentration region, and the convergent/divergent flow related to the ejection~event. We also discuss the reconstruction of the three-dimensional flow field of hairpin vortice based on the fluctuating characteristics of two-dimensional flow field. It provides an idea for the quantitative study of wall turbulence coherent structure in the formation and evolution of the hairpin vortex structure, the fusion of adjacent vortex structures and the secondary induced vortex.