TURBULENT REACTING FLOWS (PROBABILITY DENSITY, MIXING LAYERS, JETS, PLUG FLOW REACTORS, MONTE CARLO METHOD)

A numerical study of two-dimensional shear flow under reacting and non-reacting, isothermal, incompressible turbulent flows is presented. The problem of mixing and reaction in a one-dimensional plug flow reactor is also studied numerically. The shear flows under considerations are: two stream mixing layers, a plane jet, an axisymmetric jet, and two-concentric jets. The reacting flow calculations involve the gaseous chemical reaction between traces of O(,3) and NO in a carrier gas of N(,2) and the aqueous reaction between traces of HCl and NaOH diluted in water. In the non-reacting flow calculations various turbulence models are employed and validated against experimental data. These models are then used in reacting flow calculations where comparison with experimental data are also made. The flows studies here have the advantage that the chemical aspects of the problem are decoupled from the turbulence and permit to carry out an evaluation of different models for the chemical reaction rate.

A mean reaction rate model, second-order closure models, and a pdf formulation have been employed to calculate the mean reactant conversion rate. It is shown that a pdf model which employs a molecular mixing frequency corresponding to the small scale eddies yields the best overall agreement with the experimental data for a variety of flows. Despite this qualitative agreement the results suggest the need for better models which account for more accurate representation of molecular mixing.

The advantages and shortcomings of the models employed in this thesis are described, and some suggestions for future work are given.