Modeling Variable Density and Radiation Effects in Turbulent Flames with Fast Chemistry
The thesis focuses on the less known, but important, aspects of turbulent combustion, namely the variable density and radiation effects. A fundamental discussion of the basic physical phenomena involved in the pressure-density interactions is provided. Current modeling approaches are discussed and simple modifications of the k - .epsilon. system accounting for pressure-scalar, pressure-velocity, and dilatation effects are proposed for fast chemistry diffusion and premixed flames subject to pressure gradients. Substantial prediction improvements of the flames have been achieved. Nonequilibrium and radiation effects in practical combustors are evaluated using strained flamelet approximation and simple models for soot formation, burnout and radiation, and gas radiation, together with the proposed k - .epsilon. buoyant scalar transport model. Considering the complex physical and chemical interactions involved and complex flow geometry the global properties of the combustor and the radiative heat transfer are well predicted.