Shear Layer Interactions in the Helical Hydrodynamic Structures of Swirling, Reacting Jets

Swirling jets~with density stratification~are~a canonical~combustor~flow field.~ This~work consisted of coupled experimental and theoretical analysis of~the spatial structure of the most amplified modes in~an annular jet, with a specific focus on the~radial~mode shapes~of the shear layer disturbances, which we characterize as inner shear layer (ISL) motion relative to outer shear layer (OSL) motion.~ The stability analysis identifies spatial structures dominated by~ISL motion, modes dominated by OSL~motion, and modes with mixed ISL and OSL motion.~ These mixed modes are further classified as sinuous or varicose radial structures, depending on the relative motions of the two shear layers.~~The presence and spatial dependencies of~these~spatial modes are demonstrated~experimentally with a 5 kHz stereo PIV measurement of a reacting swirling jet.~ In the experiment, we demonstrate that external excitations of various spatial configurations can be used to elicit hydrodynamic responses~of axisymmetric and helical motions in~either the ISL, the OSL, or the sinuous or varicose radial modes.