Towards the optimization of a pulsatile three-stream coaxial airblast injector

Abstract

A large-scale parametric air–water test stand (AWTS) study involving more than 40 evaluations was carried out for the purposes of three-stream airblast reactor feed injector characterization and optimization; a subset of seven air stream combinations is discussed here. The role of CFD as a supplement to, or a replacement for, air–water testing is of great industrial interest. To this end a set of CFD simulations was carried out to complement the AWTS study. Pressure responses, spray opening characteristics near the feed injector face, and spray distribution were primary measures for both the AWTS and CFD programs. It was found that, over the range of variables studied, there was somewhat of a match between CFD and AWTS results. A self-exciting, pulsatile spray pattern was achieved in CFD and AWTS (frequencies between 75 and 600 Hz), and an interesting transition in spray bursting character occurred at moderate inner air flows. The oscillatory flow pattern mimics prior work in terms of the energy of the fluctuations, but the fact that the present fluctuations occur at an order of magnitude lower frequency is apparently related to the comparatively low gas/liquid momentum ratio in the current study. Overall, it is shown that the CFD method contained herein can be used to supplement, but not replace, air–water testing for said injector configuration.