| A new stochastic mixing model, termed the Lagrangian Linear Eddy Model (LLE), has been developed and validated for application in turbulent mixing and reaction simulations. The model is based on the Linear Eddy Model of Kerstein, 1988. In the new LLE, the scalar fields are represented by Lagrangian particles which follow the local flow. Each Lagrangian particle contains a high-resolution, one-dimensional description of the scalar field. Within this local one-dimensional description, both small scale turbulent advection processes and molecular diffusion are realistically represented. Flow field characteristics governing the scalar mixing are obtained from the results of the numerically simulation velocity field.; The present work describes the development of the new model and its deviation from currently used mixing models. The model is incorporated in a multidimensional computational fluid dynamics code and validated against experimental data obtained in pipe flow.; The model is then applied to mixing in pipe flow to study mechanisms of scalar mixing. By changing model parameters, the model successfully resolves discrepancies on the rate of scalar variance decay between experiments and other modeling studies. In particular, the model illustrates the importance of near-wall effects (the boundary layer) on the rate of scalar variance decay. In addition, parametric studies involving particle resolution, mechanistic variations in model processes, and flow field turbulence properties (turbulent kinetic energy, turbulent length and time scales) provide insight into the physics of turbulent mixing. |
