Studies on flow field, and instabilities in a large diameter opposed jet burner

Abstract

This work reports studies on flow fields, and instabilities exhibited by opposed jets at equal momenta, for Reynolds numbers (Re) ranging from 178 to 5000 using a large diameter counterflow jet setup. Flow instability investigations were conducted over a range of aspect ratios (α) too. This study identifies the regions of bi-stability and those of oscillatory stagnation plane offsets identified by Re. Experiments on flow field were carried out using particle image velocimetry technique, and the paper presents the axial and radial velocity profiles at various locations as well as their gradients. A decreasing trend in stagnation plane displacements with the Reynolds number was observed. The experiments in comparison with the past literature suggest a possible dependence of the stagnation plane displacements on a nozzle-exit diameter. The trends in maximum stagnation plane displacements (δmax), as well as the critical Reynolds numbers (Recr) with aspect ratios (α), are analyzed and compared. The flow field studies reveal the need for two dimensional axisymmetric simulations with realistic velocity boundary conditions to predict opposed jet flow phenomena accurately. Reacting flow instability studies were also carried out for equal momenta using methane-air and ethylene–air flames at various aspect ratios. The results show an enhanced bistability for ethylene–air flames over methane–air flames.