Chapter 5 - Direct simulation of primary atomization

Abstract

Primary atomization is a process of the formation of ligaments and drops by an atomizer. The fuel spray is a special challenge in the field of fluid mechanics. The spray is a complex multiphase flow that cannot be experimentally observed in full detail. The spray behavior is governed by a wide range of parameters, including the injection system, fuel properties, and surrounding flow. The difficulty in experiments is that the numerous droplets reflect light, obscuring the clear views of the atomization process. Dense sprays and nonspherical drops also make quantitative data difficult to obtain with laser-based diagnostics. An alternative approach is to use direct numerical simulation (DNS), but the disadvantage is that DNS is capable of simulating only a small part of the spray. In contrast to the traditional DNS, the simulation of two phases requires very advanced numerical techniques for handling the deforming free surface. This chapter investigates the initial spray breakup process providing information about the dense spray core. This is based on Navier–Stokes equations. This simulation approach is better than the earlier ones in terms of the efficiency and accuracy of the code. The direct-interface tracking is used to simulate the evolution of liquid jets and sheets into drops. The three-dimensional transient calculation tracks the interface evolution through droplet formation and breakup. Current spray models in multidimensional computational fluid dynamics (CFD) codes achieve moderately good results under a limited range of conditions by speculating on the atomization process and including adjustable parameters.