High-Fidelity Simulation of Liquid Sprays

These types of liquid sprays are most commonly observed in Direct-Injection IC engines. Liquid sprays are formed through the 'atomization’ process as seen above. Fundamental understanding of the mechanisms that drive atomization remains elusive despite decades of reserch. By employing high accuracy methods along with highly resolved grids, we are obtaining new insights into these flows.

Challenges and Solutions

Research progress in the field has been slow as these phenomena are challenging to study -

1. Experimental Challenges

   1. These happen over very small lengths and over very short time periods

   2. High droplet density makes optical investigation difficult

2. Computational Challenges

   1. Turbulence - both inside and outside the nozzle

   2. Wide range of length scales - turbulent scales << droplet sizes << domain size

Traditionally computational studeis have relied on lower order approximations and phenomenological models. We are using high-fidelity numerical methods and leveraging high-performance clusters to overcome these computational challenges.

Flaws in Traditional Modeling Approaches

Over the last 2-3 decades these flows have been studied and modeled under the linear stability framework. Popularity of this approach has spread from academia to industry. Through our simulations and flow analysis, we are discovering that this modeling approach is not applicable for real atomizing flows.

Effect of Nozzle Features on Spray Formation

The spray formation is extremely sensitive to flow development inside the nozzle (and hence the nozzle geometry). These nozzles are very small (~0.1mm) and therefore have relatively large manufacturing defects. Due to these imperfections in the nozzles and sensitivity of flow to these imperfections, it is important to characterize how these nozzle features affect the spray.

Characterization of Liquid Sprays

Three spray ‘regimes’ have been identified based on momentum-coupling betweeen gas and liquid phases.