Numerical prediction of air-assisted primary atomization using Smoothed Particle Hydrodynamics

Abstract

The well defined atomization of liquid fuels plays a key role in the combustion process of civil jet engines, in particular for minimizing toxic emissions. Presently, the breakup mechanisms leading to a wide range of droplet sizes and trajectories are not understood in detail. Furthermore, reliable numerical predictions have not been feasible due to the enormous computational costs associated with the simulation of air-assisted atomization. In this paper we present a Direct Numerical Simulation (DNS) of an experimentally investigated planar prefilming air-blast atomizer at one operating point. The numerical investigation is carried out using the Smoothed Particle Hydrodynamics (SPH) method. The spatial resolution of 5 µm yields a domain size of 1.2 billion particles. Due to the superior serial and parallel performance of the method, 122 channel flow-through times of the air flow could be realized consuming a rather small amount of computational resources. Within the simulated physical period of time of 14.6 ms, two main breakup events could be detected. As a converged statistical analysis of the resulting fuel spray properties is not possible, the quantitative comparison to the experimental findings is based on single event statistics. In this work we analyze the characteristic volumetric droplet diameters DV0.1,DV0.5 and DV0.9 and the Sauter Mean Diameter D32. Both quantitatively as well as with regard to the phenomenology of the breakup processes, the simulation matches extremely well the experimental observations. This work demonstrates, that reliable simulations of air-assisted atomization have come into reach by combining the highly efficient numerical method SPH with massive computing power.