Spray trajectory and 3D droplets distribution of liquid jet in crossflow with digital inline holography

Abstract

Liquid jet in crossflow (LJCF) has a wide application in the actual engine engineering. This article presents an experimental investigation of a water jet transversely injected into a subsonic crossflow through digital inline holographic imaging, and presents the relationship between the column trajectory and the downstream droplet distribution. A phenomenological analysis based on high-speed digital inline holography (DIH) with the frequency of 25 kHz is presented to interpret the source of droplets with different sizes in the bag breakup mode and the shear breakup mode. High-resolution DIH with a spatial resolution of 5.5μ m is applied to measure breakup point, droplet size, and location under 30 mm downstream of the orifice. The experiment is carried out under normal temperature and pressure. Gas Weber number Weg varies from 11 to 67, and the liquid to gas momentum ratio q changes from 10 to 28, which are mainly under bag breakup and multi-mode breakup regime. Crossflow velocity profiles are also measured. Liquid penetration were obtained and fitted through spray pattern under x/dj<10 and through downstream droplet statistics under 12<x/dj<70 separately. Under the cases studied, spray penetration evaluated by droplet statistics is larger than that evaluated through spray pattern. In addition, droplet size is relative large in the core region of the spray under higher Weg, possibly due to the presence of vortices in the core region and stronger aerodynamic effects at the periphery of spray. This research presents the quantification of the primary breakup process and corresponding three-dimensional (3D) downstream SMD distribution simultaneously, which helps improve the understanding of spray evolution in crossflow.