A study of turbulent diffusion flames formed by planar fuel injection into the wake formation region of a slender square cylinder

Abstract

The present work describes the experimental and numerical investigation of turbulent reacting wake flows formed by planar fuel-jet injection into the wake formation region of a confined two-dimensional square cylinder. Complementary studies of the counterpart isothermal air-injected wakes facilitated a discussion on the effect of injection and reaction on near and far wake development. Detailed measurements of turbulent velocities, temperatures, and statistics were obtained by laser velocimetry and thin, digitally compensated thermocouples for a number of short, ultralean, low fuel-air velocity ratio (FAVR) flames. The measurements highlighted the principal characteristics of slender bluff-body diffusion flame stabilization and identified differences and similarities with respect to axisymmetric bluff-body flame configurations regarding entrainment, vortex, and flame lengths, temperature and turbulence distributions, and large-scale vortex activity. In the numerical work, large eddy simulations of the reacting wake flows were performed employing a partial equilibrium/two-scalar exponential PDF combustion model applied at the subgrid level. Statistical independence of the joint PDF scalars was relaxed and the appropriate SGS moment equations were solved. The subgrid scale motions were modeled with a first-order closure using the solution of an equation for the SGS energy. Comparisons between simulations and measurements indicated the ability of the model to reproduce the experimentally observed variations in the mean and turbulent fields for a range of FAVR values and two Reynolds numbers. The method resolved important large-scale features of the isothermal and reacting flows, thus allowing a more effective exploitation of the combustion model and clearly out-performed a standard k-e/β -PDF procedure.