Modeling of Turbulent Sooting Flames

Abstract

Modeling multiphase particles in turbulent fluid environment is a challenging task. To accurately describe the size distribution, a large number of scalars need to be transported at each time-step. Add to that the heat release and species mass fraction changes from nonlinear combustion chemistry reactions, and you have a tightly coupled set of equations that describe the (i) turbulence, (ii) chemistry, and (iii) soot particle interactions (physical agglomeration and surface chemistry reactions). Uncertainty in any one of these models will inadvertently introduce errors of up to a few orders of magnitude in predicted soot quantities. The objective of this thesis is to investigate the effect of turbulence and chemistry on soot evolution with respect to different soot aerosol models and to develop accurate models for simulating soot evolution in aircraft combustors. To investigate the effect of small scale turbulence time-scales on soot evolution, a partially-stirred reactor (PaSR) configuration is used and coupled with soot models from semi-empirical to detailed statistical models. Differences in soot property predictions including soot particle diameter and number density among the soot models are highlighted. The soot models will then be used to simulate the turbulent sooting flame in an aircraft swirl combustor to determine the large scale soot-turbulence-chemistry interactions. Highlights of this study include the differences in location of bulk soot mass production in the combustor using different soot models. A realistic aircraft combustor operating condition is simulated using a state-of-the-art minimally dissipative turbulent combustion solver and soot method of moments to investigate pressure scaling and soot evolution in different operating conditions. A separate hydrodynamic scaling is introduced to the pressure scaling, in addition to thermochemical scaling from previous studies. Finally, a Fourier analysis of soot evolution in the combustor will be discussed. A lower sooting frequency mode is found in the combustor, separate from the dominant fluid flow frequency mode that could affect statistical data collection for soot properties in turbulent sooting flame simulations.