Air-blast atomization of liquid films: Modeling of droplet size distribution based on bag-breakup mechanism

Wayne State University, Detroit MI

Investigators

Abstract

Understanding how liquids break into droplets, a process known as atomization, is crucial for many natural and industrial processes from rainfall to fuel injection in engines. One widely used method, air-blast atomization of liquid films, relies on high-speed gas flows to produce fine droplets. These droplets are essential in applications such as power generation, agricultural spraying, and surface coating. However, accurately predicting the size of these droplets remains a challenge due to the complex nature of the breakup process. Current models often overlook key mechanisms and lack the precision needed for reliable prediction. This award addresses that gap by developing a new, physics-based model that significantly improves the accuracy of droplet size distribution predictions. The research also supports the national interest by advancing scientific understanding in fluid dynamics, enhancing technologies in aerospace and chemical industries, and expanding educational and outreach opportunities. This project focuses on the air-blast atomization of liquid films, aiming to develop a predictive, physics-based model for spray droplet size distribution with an emphasis on the bag-breakup mechanism. Traditional models based on Kelvin-Helmholtz and Rayleigh-Taylor instabilities often fail to capture the fine droplets produced by bag breakup, a dominant mode of secondary atomization. To address this limitation, the project combines high-fidelity Direct Numerical Simulations (DNS) with experimental validation to investigate how gas-induced transverse instabilities generate rectangular liquid films that inflate and rupture into droplets. The research is organized into three objectives: (1) characterizing gas-driven transverse fluctuations in planar liquid films, (2) simulating the deformation and bag breakup of rectangular films under high-speed gas flow, and (3) developing a mechanistic model that integrates these findings to predict droplet size distributions. The model captures key breakup processes, including hole formation and collision, fingering instability, and rim fragmentation. The project’s outcomes will enhance the accuracy of droplet size predictions across a wide range of conditions, improving spray system design in aerospace, chemical, and agricultural applications. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.