Modal analysis and interface tracking for multiphase flows*

The primary breakup of a liquid core by an airblast atomizer is a complex phenomenon involving several instabilities that result in droplet generation and dispersion. We use back-lit imaging to distinguish the liquid-gas interface of a liquid-gas airblast atomizer at high temporal and spatial resolutions and employ Dynamic Mode Decomposition (DMD) to study the shape and frequency of instabilities of a liquid jet.  Because DMD is not suitable for interface tracking, we develop a data-driven two-step approach using the optical sensor data for the reconstruction and prediction of the location of the liquid-gas interface. The method uses DMD on the optical flow field estimated from image snapshot pairs. We demonstrate our method to a representative toy problem of an oscillating drop and on the primary atomization of a numerical planar liquid jet. Finally, we apply our method to the experimental liquid jet from the coaxial airblast atomizer using back-lit imaging. Our method is able to accurately reconstruct and predict the flow and preserves the sharpness of the fluid interface.