Change in Vortex Breakdown Mode and It’s Influence on Flame Shape of a Co/counter Concentric Swirling Streams

The present study experimentally investigates the flow field of co/counter-swirling stream under non-reacting and reacting conditions by varying the momentum ratio (Mratio). We utilized two-dimensional particle image velocimetry (2D-PIV) to examine the flow field. For non-reacting cases, co-swirl shows slender recirculation zone (RZ) at low Mratio. The volume of RZ increases slowly till Mratio = 1.1. However, a drastic change in flow field is observed after Mratio = 1.1. In comparison, the counter-swirl configuration has a small ellipsoidal RZ at low Mratio. Similar to co-swirl, a drastic change in flow topology occurs after Mratio = 1.7. This change in flame topology indicates the change in breakdown mode. PIV images indicate two types of breakdowns: bubble (BVB) and conical (CVB) vortex breakdown. This breakdown modes can be observed in reacting cases also. It is observed that the flame shape strongly depends on breakdown mode. The present study unravels few interesting features of the flow field of co/counter-swirling streams.