Large Eddy Simulation of Primary and Secondary Breakup Using a Multiscale Euler-Lagrange Method

• Applicant: Professor Dr.-Ing. Markus Klein
• Subject Area: Fluid Mechanics
• Term: since 2014
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 252571588

Fluid atomization describes the disintegration of a compact liquid volume into many small drops. It is the starting point for many technical processes with a wide range of applications in technology, medicine and agriculture. The design and upscaling of atomizers on an empirical basis is still common practice. While predictive simulation techniques are well established in other areas of computational fluid dynamics, existing atomization models typically require calibration using detailed measurements for each operating condition. As a consequence, the spray characteristic is often prescribed rather than predicted and hence the possibilities of state of the art simulation methods are not fully used. The large-eddy simulation technique (LES) represents a model for computing turbulent flows, which has the potential to describe the atomization process with good accuracy. When deriving the LES filtered two-phase flow (liquid / gas) equations, several unclosed terms occur. Reliable modeling of these terms is still not established and was the subject of the first part of this proposal. However, drops with diameter of the order of the LES filter width cannot be captured within the used Volume-of-Fluid methodology and they will now be considered in the context of Lagrangian particle tracking. The goal of this second phase is therefore the development of a closed modeling chain of the complete atomization process, consisting of primary and secondary breakup, in the context of a multiscale Euler-Lagrange framework.The project can be divided into three main parts. The first phase will deal with the modeling of the direct ejection of primary drops that are smaller than the LES filter width without undergoing a secondary breakup process. In the second phase, an established secondary breakup model from literature will be used and validated in the framework of this project, such that droplet collision, breakup and coalescence can be taken into account. This is called four-way coupling, while the two-way coupling describes the feedback effect of drops on the continuous phase. There is great need for research related to two-way coupling. This holds in particular true in the context of this work where the droplet diameter can be at the order of the filter width and hence the interaction of both phases cannot be ignored. In the last part of the project, the calibration and validation of the overall model will take place, using both the DNS database of the first part of the project and experimental data from literature. With successful validation the result of the project will be a practicable simulation tool for the LES of atomization processes. This is to be validated in a final step by calculating a pressure atomizer with complex nozzle geometry, which has been experimentally characterized in literature, using OpenFOAM in combination with the developed modelling strategy.

• DFG Programme: Research Grants