A twin-fluid pneumatic injector system with coaxial liquid and air streams mixed slightly upstream of the outlet, is studied in a cross-flow arrangement to understand its working principle. The gap between the orifice and the liquid tube, where the air and liquid cross-flow occurs, is known to determine the modes of working of the atomizer for the given operating flow rates of air and liquid. The two distinct modes, namely the flow focusing (FF) and flow blurring (FB) are observed in the present study, and the transition from FF to FB mode is explored using optical visualization. The characteristics of the internal two-phase flow mixing that occurs due to backflow recirculation in FB mode are also investigated by performing large eddy simulation (LES) using the volume of fluid (VoF) approach. The results of the numerical simulation are validated with experimental observations for the length of backflow recirculation observed in the liquid tube. The present study demonstrates the development of multiple microjets, which explains experimental observations of the lack of core jet and the almost uniform distribution of radial Sauter mean diameter (SMD) reported in the literature. The high-resolution backlit image of a scaled-up transparent injector with a 6 mm orifice diameter validates the numerical results that describe the internal two-phase flow.

对双流体气动注射器系统进行了研究，以同轴流体和气流在出口上游稍微混合的方式进行研究，以了解其工作原理。已知孔口和液体管之间会发生空气和液体交叉流动的间隙，对于给定的空气和液体工作流速，该间隙可确定雾化器的工作模式。在本研究中观察到两种不同的模式，即流动聚焦（FF）和流动模糊（FB），并使用光学可视化探索了从FF到FB模式的过渡。通过使用流体体积（VoF）方法执行大型涡流模拟（LES），还研究了由于FB模式下的回流造成的内部两相流混合的特性。数值模拟的结果已通过实验观察验证了在液体管中观察到的回流长度。本研究表明了多种微射流的发展，这解释了文献中报道的缺乏芯射流和径向Sauter平均直径（SMD）几乎均匀分布的实验观察。孔径为6 mm的按比例放大的透明进样器的高分辨率背光图像验证了描述内部两相流的数值结果。这解释了文献中报道的缺乏芯射流和径向索特平均直径（SMD）几乎均匀分布的实验观察结果。孔径为6 mm的按比例放大的透明进样器的高分辨率背光图像验证了描述内部两相流的数值结果。这解释了文献中报道的缺乏芯射流和径向索特平均直径（SMD）几乎均匀分布的实验观察结果。孔径为6 mm的按比例放大的透明进样器的高分辨率背光图像验证了描述内部两相流的数值结果。