RANS Simulation of Turbulent Diffusive Combustion using Open Foam

Schemes to write the flow equations in discreet form, solution solvers, pre and post data processing utilities provided by OpenFoam libraries, are used to build a finite volume executable for simulating a low speed, turbulent and rate controlled diffusive CH4-Air combustion. Unsteady Favre’s averaged turbulent conservation equations (total mass, momentum, energy and species mass fractions), are used to describe the combustion gas dynamics, and to handle turbulence a modified k-e model is applied. Several global kinetic mechanisms, one step, two and four steps have been considered to describe the oxidation process of CH4 in a free jet type flame. The interaction between chemistry and turbulence, is modeled according to the partially stirred reactor (PaSR) concept. To improve convergence and accuracy in solving low speed fluid dynamic equations, a pressure implicit with splitting of operators (PISO) technique extended to cover high temperature flows, is utilized. The exponential dependence of the chemical kinetics from temperature, makes stiffs the ODE’s needed to determine source average values with which the species conservation equations are solved. To deal with the stiffness issue, OpenFoam provides numerical schemes that guaranties the stability of the computation. Comparisons between results of numerical simulations and experimental data obtained with the benchmark known as flame “D”, are presented.