New insights in the role of turbulence for simulating primary breakup of prefilming airblast atomization
Katharina Warncke  1@  , Amsini Sadiki  1@  , Johannes Janicka  1@  
1 : Department of Energy and Power Plant Technology, Technische Universität Darmstadt
Otto-Berndt-Straße 3, 64287 Darmstadt -  Germany

Details of the liquid fuel disintegration in aircraft engines are not completely understood. Complex flows, a dense spray and fine liquid droplets demand high resolution and limit experimental and numerical studies. Getting access to the physical mechanisms and spray characteristics of the initial atomization step, the embedded DNS methodology has been proven to be a valuable tool: A Direct Numerical Simulation (DNS) of the primary breakup is embedded in a Large Eddy Simulation (LES) of the atomizer, reducing computational costs and making expensive DNS feasible for technical relevant applications. A specific feature of the method is the consideration of a realistic turbulent nozzle flow instead of setting constant values at the boundaries of the DNS. In this study the relevance of the inclusion of the turbulent nozzle flow in primary breakup simulations of airblast atomization is demonstrated. Therefore, a sensitivity study for a planar prefilming airblast atomizer is conducted applying one operating point and two different sets of boundary data for the embedded domain. The first set consists of time-varying data from LES of the planar atomizer while the second one considers time-averaged values of the first set. The last mentioned set mimics a constant profile at the boundaries. 3D DNS of both cases is performed applying the Volume of Fluid method. Analyses of the liquid film development and spray characteristics relating to the different amounts of turbulent scales in the gaseous flow are presented. The results indicate a non-neglectable influence of turbulence on the breakup. In particular, the results show that turbulent scales in the gaseous flow increase the amount of fine droplets. The SMD is reduced from 182 µm to 148 µm and the atomized mass is increased by 10 % if a turbulent flow is considered. Therefore, the effects of turbulence should be considered.

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