Combined optical connectivity and optical flow velocimetry measurement of interfacial velocity of a liquid jet in gas crossflow

Abstract

Liquid jet in crossflow (LJIC) is a process in which a high-speed gas crossflow deforms and shears a continuous liquid flow into tiny droplets. This study quantifies the liquid surface motion of LJIC during the primary breakup process, which has not been quantified due to the optical limitation close to the nozzle exit. The interfacial velocity of a breaking liquid jet indicates the local interaction of the gas and liquid flows and determines the initial velocity of the stripped droplets. The local interfacial liquid velocities of LJIC have only been estimated from theoretical and computational studies, which have not been evaluated from measurements. Optical Connectivity (OC) introduces a laser beam through an atomiser nozzle and relies on total internal reflection at the liquid interface to propagate the laser light inside the continuous liquid to record the instantaneous features of the interface of the continuous liquid during the primary atomisation at the near nozzle region through imaging of the emitted fluorescent intensity from the liquid flow. The current study combines Optical Connectivity with Optical Flow Velocimetry (OFV) to quantify the time-dependent, local interfacial velocity of the liquid interface structures of the LJIC for gas Weber numbers between 14.9 - 112.6 and liquid-to-gas momentum ratios between 2.1 - 36.4. The combined OC-OFV measurements of the spatial distribution of the mean and fluctuating values of the different components of the liquid interfacial velocity of LJIC demonstrate how the gaseous shear and liquid jet geometry interact to influence the atomisation process.