Combined visualisation of cavitation and vortical structures in a real-size optical diesel injector
Combined visualisation of cavitation and vortical structures in a real-size optical diesel injector
复制标题
DOI：
10.1007/s00348-020-03096-1
复制
发表时间：
2020-12
影响因子：
2.4
通讯作者：
I. Karathanassis;Joonsik Hwang;P. Koukouvinis;L. Pickett;M. Gavaises
中科院分区：
文献类型：
--
作者：
I. Karathanassis;Joonsik Hwang;P. Koukouvinis;L. Pickett;M. Gavaises
摘要本文提出了一种由漫射背光照明（DBI）和纹影成像相结合的高速流动可视化装置，用于描述真实尺寸的光学喷油器中的高瞬态两相流。这两种技术的不同照明性质，分别是漫射光和平行光，允许捕获由于孔内存在界面和密度梯度而引起的折射率梯度。因此，可以同时可视化囊和喷射器孔内的空化和二次流运动的开始。利用装配有单孔透明尖端（ECN喷雾D）的柴油喷射器在700-900巴的喷射压力和1-20巴范围内的环境压力下进行实验。在100，000 fps下获得的高速DBI图像显示，由于其锥形布局，孔口轻微空化，主要在制造缺陷区域产生相对恒定的空腔片。尽管如此，纹影图像在相同的帧速率表明，大量的短寿命的涡流出现在不同的尺度在液囊和喷嘴区域在整个持续时间的喷射周期，但涡流不一定会导致相变。相干涡旋结构的大小和精确位置对喷射器出口下游出现的喷雾的动态特性有可测量的影响，导致其锥角变化的明显差异取决于所检查的喷射和环境压力。图形摘要
AbstractA high-speed flow visualisation set-up comprising of combined diffuse backlight illumination (DBI) and schlieren imaging has been developed to illustrate the highly transient, two-phase flow arising in a real-size optical fuel injector. The different illumination nature of the two techniques, diffuse and parallel light respectively, allows for the capturing of refractive-index gradients due to the presence of both interfaces and density gradients within the orifice. Hence, the onset of cavitation and secondary-flow motion within the sac and injector hole can be concurrently visualised. Experiments were conducted utilising a diesel injector fitted with a single-hole transparent tip (ECN spray D) at injection pressures of 700–900 bar and ambient pressures in the range of 1–20 bar. High-speed DBI images obtained at 100,000 fps revealed that the orifice, due to its tapered layout, is mildly cavitating with relatively constant cavity sheets arising mainly in regions of manufacturing imperfections. Nevertheless, schlieren images obtained at the same frame rate demonstrated that a multitude of vortices with short lifetimes arise at different scales in the sac and nozzle regions during the entire duration of the injection cycle but the vortices do not necessarily result in phase change. The magnitude and exact location of coherent vortical structures have a measurable influence on the dynamics of the spray emerging downstream the injector outlet, leading to distinct differences in the variation of its cone angle depending on the injection and ambient pressures examined.Graphic abstract