This dissertation presents the development and validation of the One Dimensional Turbulence (ODT) multiphase model in the Lagrangian reference frame. ODT is a stochastic model that captures the full range of length and time scales and provides statistical information on fine-scale turbulent-particle mixing and transport at low computational cost. The flow evolution is governed by a deterministic solution of the viscous processes and a stochastic representation of advection through stochastic domain mapping processes. The three algorithms for Lagrangian particle transport are presented within the context of the ODT approach. The Type-I and -C models consider the particle-eddy interaction as instantaneous and continuous change of the particle position and velocity, respectively. The Type-IC model combines the features of the Type-I and -C models. The models are applied to the multiphase flows in the homogeneous decaying turbulence and turbulent round jet. Particle dispersion, dispersion coefficients, and velocity statistics are predicted and compared with experimental data. The models accurately reproduces the experimental data sets and capture particle inertial effects and trajectory crossing effect. A new adjustable particle parameter is introduced into the ODT model, and sensitivity analysis is performed to facilitate parameter estimation and selection. A novel algorithm of the two-way momentum coupling between the particle and carrier phases is developed in the ODT multiphase model. Momentum exchange between the phases is accounted for through particle source terms in the viscous diffusion. The source term is implemented in eddy events through a new kernel transformation and an iterative procedure is required for eddy selection. This model is applied to a particle-laden turbulent jet flow, and simulation results are compared with experimental measurements. The effect of particle addition on the velocities of the gas phase is investigated. The development of particle velocity and particle number distribution are illustrated. The simulation results indicate that the model qualitatively captures the turbulent modulation with the presence of difference particle classes with different solid loadings. The model is then extended to simulate temperature evolution of the particles in a nonisothermal hot jet, in which heat transfer between the particles and gas is considered. The flow is bounded by a wall on the one side of the domain. The simulations are performed over a range of particle inertia and thermal relaxation time scales and different initial particle locations. The present study investigates the post-blast-phase mixing between the particles, the environment that is intended to heat them up, and the ambient environment that dilutes the jet flow. The results indicate that the model can qualitatively predict the important particle statistics in jet flame.

The mechanism of flame propagation in fuel beds of wildland fires is important to understand and quantify fire spread rates. Fires spread by radiative and convective heating and often require direct flame contact to achieve ignition. The flame interface in an advancing fire is unsteady and turbulent, making study of intermittent flames in complex fuels difficult. This thesis applies the one-dimensional turbulence (ODT) model to a study of flame propagation by simulating a lab-scale fire representative of the flame interface in a fuel bed and incorporating solid fuel particles into the ODT code. The ODT model is able to resolve individual flames (a unique property of this model) and provide realistic turbulent statistics. ODT solves diffusion-reaction equations on a line-of-sight that is advanced either in time or in one spatial direction (perpendicular to the line-of-sight). Turbulent advection is modeled through stochastic domain mapping processes. A vertical wall fire, in which ethylene fuel is slowly fed through a porous ceramic, is modeled to investigate an unsteady turbulent flame front in a controlled environment. Simulations of this configuration are performed using a spatial formulation of the ODT model, where the ODT line is perpendicular to the wall and is advanced up the wall. Simulations include radiation and soot effects and are compared to experimental temperature data taken over a range of fuel flow rates. Flame structure, velocities, and temperature statistics are reported. The ODT model is shown to capture the evolution of the flame and describe the intermittent properties at the flame edge, though temperature fluctuations are somewhat over predicted. A solid particle devolatilization model was included in the ODT code to study the convective heating of unburnt solid fuels through direct flame contact. Here the particles are treated as sweet gum hardwood and a single-reaction, first order decomposition model is used to simulate the devolatilization rates. Only preliminary results were presented for a simple case, but this extension of the ODT model presents new opportunities for future research.

Turbulent combustion systems are physically complex processes that involve many interdependent phenomena---including turbulent fluid dynamics, multi-component mass transfer, convective and radiative heat transfer, and multiphase flow---that occur over a wide range of length and time scales. Modeling and simulation studies complement experimental work by implementing and validating models and providing predictive capabilities, but current software tools are often limited by a lack of standardization and best practices, non-robust implementation, or over-specialization. Some topics in combustion CFD research, notably radiative heat transfer and soot modeling, are critically underrepresented in simulation studies as a result of software limitations. This project establishes and develops three computational tools designed for use in combustion CFD: the ODT code implements the one-dimensional turbulence (ODT) model in its most reliable form, increasing its potential for application to turbulent flow problems of interest to engineers; RadLib is a standalone library of validated radiative property models intended for application to combustion systems; and SootLib is a library of validated models for soot chemistry and particle size distribution treatments, including four moment methods and one sectional model. All three tools are open-source, cross-platform model implementations that incorporate aspects of modern software design intended to make them flexible, consistent, and easy to use and expand upon. The tools developed in this project provide researchers with convenient access to modeling tools for complex phenomena that might otherwise require significant investments of time and resources to implement individually. They also provide established frameworks on which new models can be developed and communicated, offering unparalleled potential for comparative and parametric studies of combustion processes.