ID 22

A HYBRID APPROACH FOR THE NUMERICAL SIMULATION OF FLUID PHASE DISPERSION PROCESSES

 

Abstract:

This numerical work presents a novel approach to model primary atomization. Innumerable processes require the dispersion of one fluid into another such as fuel sprays in combustion, liquid sprays in cooling towers, spray dryers etc. The primary goal is the creation of a large specific inter-phase boundary area by fine dispersion of a fluid into small droplets. Many influential factors determine the particle size distribution and subsequent heat and mass transfer between the particles and the continuous phase.

However, the initial process that disrupts a continuous flow, or jet, of a fluid into filaments, ligaments and droplets is highly dependent on geometric details of the nozzle as well as flow parameters in the nozzle and around it. Therefore, predictive simulations of the primary breakup often times resolve the initial and intermediate structures that are eventually broken down into (fluid) particles using the “volume of fluid” (VOF) Eulerian multi-phase fluid flow simulation approach. Since there usually is no clear spatial separation between primary and secondary breakup, recent work has made it possible to combine both simulation techniques in a single calculation in Ansys FLUENT CFD solver. This procedure makes the numerical prediction of nozzle flows and droplet size distributions more affordable.

We describe the components of the integrated VOF-DPM (Lagrangian) simulation setup, and present results from first validation simulations looking at liquid atomization. In the setup, important components are a robust VOF formulation, LES Turbulence model along with adaptive meshing to keep the cell count low, the identification of lumps in the VOF solution and conversion into particles in the Lagrangian framework, the concept of representative particle “parcels”, secondary breakup models and efficient parallel processing. Several examples are included.