Experimental Characterization of the Velocity Distribution in a Dynamic Impinging Sheet

Abstract

Impinging jet atomizers are essential in engineering applications, where two liquid jets collide to form a dynamic sheet that breaks into droplets, completing the atomization process. The sheet's properties (e.g., size, thickness, velocity, and geometry) are influenced by factors like impingement angle, jet velocity, and liquid properties. Since sheet formation occurs before droplet generation, modeling the sheet is critical for understanding the downstream atomization.

This present work investigates velocity distribution of a dynamic impinging sheet using experimental and theoretical approaches. Particle tracking velocimetry (PTV), combined with high-speed shadowgraph imaging, is used to measure the velocity. Experimental results of the velocity field, obtained for Reynolds numbers ranging from 362 to 430, show significant deviations from existing theoretical predictions. A revised model is proposed by incorporating friction effect over the air-sheet interface. Based on boundary layer theory in cylindrical coordinates, the new model adopts unique boundary conditions and a similarity variable to simplify and solve the governing equations numerically. The revised model predicts air boundary layer profiles and velocity distributions inside the sheet as functions of radial distance and azimuthal angle. The initial jet velocity profile, modeled as a free jet transitioning from Poiseuille flow, is also estimated.

The revised model aligns more closely with experimental observations, identifying key parameters that influence sheet behavior. This study advances the understanding of impinging sheet dynamics, offering insights for improving atomization performance in practical applications.