Hysteresis and turbulent vortex breakdown in transitional swirling jets

Vortex breakdown (VB) in unconfined swirling jets occurs as either a bubble form of vortex (BVB) or conical (CVB). This computational study examines flow features these forms for Reynolds number at which VB is accompanied by transition to turbulence ( $Re = 1000$ , based on inflow jet radius and centreline velocity). Large eddy simulations were performed with the condition Maxworthy profile models laminar, axisymmetric jet, effect varying swirl strength was investigated. BVB observed lower strengths than those CVB occurs. With increasing swirl, regular wide-open types occur. Spiral coherent structures that develop examined using spectral proper orthogonal decomposition. Further, means hysteresis studies, it established turbulent are bistable forms. Similarly, shown two also bistable. The difference recirculation zone (RZ) sizes between greatly reduced when compared laminar counterparts. postulated reason misidentification (RZ approximately shape) (spheroidal RZ) some previous studies. present highlights distinct CVB, can potentially be used towards improving designs swirl-stabilized combustors.