# Deformation and breakup of droplets in an oblique continuous air stream

## TL;DR

This experimental study explores how droplets deform and break up in an oblique air stream, revealing how initial droplet momentum, flow angle, and fluid properties influence breakup modes and critical Weber numbers.

## Contribution

The paper introduces new experimental data on droplet breakup in oblique air streams, highlighting the effects of flow angle and initial droplet momentum on breakup behavior and critical Weber numbers.

## Key findings

- Critical Weber numbers depend on flow angle, Eötvös, and Ohnesorge numbers.
- Droplet motion transitions from rectilinear to curvilinear during breakup.
- Breakup mode thresholds vary with flow orientation and droplet initial conditions.

## Abstract

We experimentally investigate the deformation and breakup of droplets interacting with an oblique continuous air stream. A high-speed imaging system is employed to record the trajectories and topological changes of the droplets of different liquids. The droplet size, the orientation of the air nozzle to the horizontal and fluid properties (surface tension and viscosity) are varied to study different breakup modes. We found that droplet possessing initial momentum prior to entering the continuous air stream exhibits a variation in the required Weber number for the vibrational to the bag breakup transition with a change in the angle of the air stream. The critical Weber numbers $(We_{cr})$ for the bag-type breakup are obtained as a function of the E\"{o}tv\"{o}s number $(Eo)$, angle of inclination of the air stream $(\alpha)$ and the Ohnesorge number $(Oh)$. It is found that although the droplet follows a rectilinear motion initially that transforms to a curvilinear motion at later times when the droplet undergoes topological changes. The apparent acceleration of the droplet and its size influence the critical Weber number for the bag breakup mode. The departure from the cross-flow arrangement shows a sharp decrease in the critical Weber number for the bag breakup which asymptotically reaches to a value associated with the in-line (opposed) flow configuration for the droplet breakup.