Session: 5.2.1 - Novel Measurement Techniques in Fluid Engineering I

Paper Number: 158541

158541 - Characterization of the Velocity Distribution of the Impinging Sheet 

Abstract: 

Impinging jet atomizers are essential in engineering applications, where two liquid jets collide to form a sheet that breaks into droplets, completing the atomization process. The sheet’s properties—size, thickness, velocity, and shape—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 research investigates the sheet’s thickness and velocity using experimental and theoretical approaches. Partial coherent interferometry (PCI), a non-intrusive optical technique, is used to dynamically measure sheet thickness. PCI utilizes the calibrated linear relationship between optical path difference and coherence degree. By setting the sheet in one branch of an interferometer, thickness-induced changes in the optical path appear as variations in the recorded interference pattern’s coherence. With calibration, the sheet thickness is accurately measured.

Particle tracking velocimetry (PTV), combined with shadowgraph imaging, is used to measure sheet velocity. Small seeding particles are introduced into the liquid while their motion is tracked across frames to calculate velocity. However, when particle size matches the sheet thickness, a ‘particle-induced lens effect’ distorts conventional imaging due to fluid wrapping around the particles. This effect is leveraged to achieve an extended field of view, enhancing measurement accuracy.

Experimental results, obtained for Reynolds numbers ranging from 269 to 430, show significant deviations from existing theoretical predictions of sheet thickness and velocity. To address this, a revised theoretical model is proposed, incorporating air friction effects. Based on boundary layer theory in cylindrical coordinates, the model uses 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 as functions of 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.

Presenting Author: Weixiao Shang Purdue Univ.

Presenting Author Biography: