横流中喷雾掺混流场结构研究

Investigation of Mixing Flow Field of Spray Droplets in Crossflow

关键词:  横流  喷雾  掺混流场  反旋涡对

Key words:  Crossflow  Spray droplets  Mixing flow field  Counter-rotating vortex pair

摘要:

为了获得有限空间内喷雾在横流影响下的掺混发展及机理,应用PIV系统测量了单个旋流雾化喷嘴产生的喷雾在横流中的掺混流场,实验在矩形通道内实施。获得了3种喷嘴入射角度和3种液气动量比下的掺混截面流场结构。结果表明,由于射流撞击、剪切和壁面约束作用,流场中形成前缘涡和反旋涡对,反旋涡对对掺混起了主要作用。比较不同喷嘴入射角度和液气动量比下的流场结构发现,随喷雾入射角度减小,两相作用提前发生,且反旋涡对尺度小,更利于掺混均匀；随液气动量比减小,气相作用增强,旋涡强度和尺度变小,更小的涡尺度更利于液滴均匀分布。 

Abstract:

In order to understand the evolution and mechanism of the mixing of spray droplets in crossflow in confined space, the mixing flow fields of water spray in air crossflow were measured in a rectangular duct by using a particle image velocimetry (PIV) system. The spray was generated by a pressure swirl nozzle. The velocity vector structures at different cross sections were obtained under the work conditions of three nozzle injection angles and three liquid/gas momentum flux ratios. The results show that the leading vortex pair appears due to the first impingement of the crossflow and the spray. The counter-rotating vortex pairs (CVPs) are observed during the mixing process. The CVP forms due to the shear of spray and the restraint of wall and plays an important role in influencing the mixing uniformity. It is also found that the inclined nozzle with an injection angle against the upstream crossflow allows the CVP to occur early and the CVP maintains a small size. A smaller liquid/gas momentum flux ratio also contributes to a small-scale CVP. Both the two mechanisms help to enhance the mixing uniformity.