Session: 04-31: Emissions II

Paper Number: 151330

Comprehensive Modeling of the Cause-And-Effect Chain in Aero-Engine Combustor Simulations: From Primary Breakup to Soot Formation 

Minimizing pollutant emissions remains a key challenge in the development of next-generation aero-engines. Soot emissions are of particular concern due to their significant environmental and health effects. Hence, predictive soot models are essential for fully leveraging computational fluid dynamics (CFD) as a design tool, enabling the reduction of development time and costs. While there have been ongoing efforts to enhance the accuracy of soot formation models in single-phase academic configurations, there has been limited emphasis on modeling the complete chain of physical processes involved in real aero engines, from fuel injection and atomization to mixture formation, initial soot particle formation in the primary combustion zone and, subsequent soot evolution in the post-flame region.

The primary reason for excluding the entire fuel break-up sequence from simulations is the prohibitively high computational cost. To overcome these challenges, this work explores the coupling of smoothed particle hydrodynamics (SPH) simulations for primary breakup and high-fidelity finite volume method (FVM) for reactive large eddy simulations (LES). Instead of modeling the fuel break-up process directly within the FVM, it is calculated beforehand by detailed SPH simulations of the fuel spray nozzle, benefiting from the the Lagrangian nature of this method. The air and fuel mass flows and the simulation domain for the SPH simulations are extracted from an initial FVM flow prediction of the full configuration. Detailed spray particle size distributions (PSDs) corresponding to the state after primary breakup are sampled from the SPH simulation and then used to initialize Lagrangian spray particles in the subsequent LES, where secondary breakup, evaporation and soot evolution are modeled. The configuration examined in this study consists of a single-sector aero-engine model combustion chamber, which is operated under high pressures and high preheating temperatures and incorporates a real fuel injector geometry. This setup has been experimentally investigated using advanced optical laser diagnostic methods and available data for the velocity field, the soot volume fraction and the OH* chemiluminescence are used for validation of the CFD simulations.

By varying the level of detail of the PSD prescribed in the LES, the influence on the mixture field and soot formation is investigated. This analysis provides insights into the coupling between fuel atomization and soot formation, enabling an assessment of the important characteristics of the fuel spray that need to be included in predictive CFD models. The validation of the simulation results with the experimental data shows good agreement for the velocity fields, soot distribution and flame position. While variations in the droplet distribution have only minor effects on the velocity field and flame position, incorporating detailed radial distributions of spray particle PSD and particle starting velocities from SPH simulation into the LES reveals changes in the mixing field, resulting in enhanced predictions of the soot volume fraction.

In summary, this study demonstrates the importance of accurate spray characteristics for predicting mixing, and consequently pollutant formation, in aero-engine combustors. Furthermore, the findings provide guidance on the required level of detail in prescribing spray distributions for high-fidelity combustion simulations.

Presenting Author: Philipp Koob Technical University of Darmstadt

Presenting Author Biography: Philipp Koob obtained his M.S. at the Technical University of Berlin in Engineering Science. Since 2021 he is a research associate at the Institute for Simulation of reactive Thermo-Fluid Systems at the Technical University of Darmstadt. He works in the field of emission modeling in gas turbine engines using numerical methods.

Authors:

Philipp Koob Technical University of Darmstadt
Hendrik Nicolai Technical University of Darmstadt
Andreas Lindenthal Technical University of Darmstadt
Frederic Aaron Witkind Hirth Karlsruhe Institute of Technology
Niklas Bürkle Karlsruhe Institute of Technology
Thomas Soworka German Aerospace Center
Ruud Eggels Rolls-Royce Deutschland Ltd & CO KG
Carsten Clemen Rolls-Royce Deutschland Ltd. & CO KG
Rainer Koch Karlsruhe Institute of Technology
Thomas Behrendt German Aerospace Center
Michael Schroll German Aerospace Center
Christian Hasse Technical University of Darmstadt