Sub-grid scale modeling of primary break-up for large eddy simulation in the atomizing regime

• Applicant: Professor Dr.-Ing. Michael Oevermann
• Subject Area: Fluid Mechanics
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 535882288

Spray atomization refers to the disintegration of liquid jets into droplets for high Weber and Reynolds numbers. It is a widely utilized engineering application, examples include fuel injection in engines, spray-painting, spray-drying, or metal powder production for additive manufacturing. The atomization process is usually divided into two parts: primary breakup, which comprises the initial pinch-off of liquid ligaments and droplets from the liquid core, followed by secondary breakup describing the further disintegration of those ligaments and droplets into smaller droplets until surface tension dominates and results in stable droplets. For computational fluid dynamics (CFD) simulations of atomization processes, primary breakup is often regarded as the weakest part among all the sub-models needed to describe the relevant physical mechanism and will be addressed in this project. Large eddy simulation (LES) has proven to be an accurate and affordable approach for single phase turbulent flow and there is a strong and ongoing research effort to develop predictive LES models for multiphase flow. In LES, the energy containing large scale motion is resolved directly, whereas scales smaller than a prescribed cutoff scale are taken into account via sub-grid scale (SGS) models. A promising simulation approach to perform efficient LES of spray atomization for engineering applications is to model the LES resolved flow with an Eulerian approach and small liquid structures and droplets below the LES grid scale via Lagrangian point particles. However, LES grids for spray atomization simulations of engineering applications are often so coarse that important breakup physics is not directly resolved but needs to be modeled. The predictive capability of the whole approach critically depend on the fidelity of the sub-grid scale model for primary breakup. One very few SGS models for primary breakup can be found in the literature. The proposed project aims at developing a new primary breakup model for spray atomization suitable for high-fidelity sub-grid scale closure in large eddy simulation. The model is based on a simplified version of the one-dimensional turbulence (ODT) model. The characteristic feature of the new SGS model is to represent complex break-up phenomena on the unresolved scales, which permits the use of comparatively coarse grids for engineering applications. We focus on spray atomization under high turbulence conditions, i.e. high Reynolds and Weber numbers.The performance of the model will be evaluated via comparison of simulation results with data from standard ODT, direct numerical simulation (DNS) and LES results found in the literature.

• DFG Programme: Research Grants
• International Connection: Austria
• Co-Investigator: Professor Dr.-Ing. Markus Klein
• Cooperation Partner: Dr. Mahdi Saeedipour