Mixing processes in a coaxial geometry with a central lobed mixer-nozzle

An experimental investigation was undertaken to study mixing professes in a coaxial jet, where the inner jet geometry is a lobed mixer, Various inner jet nozzle geometries were explored at three velocity ratios (3:1, 1:1, and 1:3, inner:outer). Detailed flow visualizations were performed and have been reported elsewhere. Results of velocity measurements of one of the nozzles that generates strong streamwise vortices are presented, Three components of velocity were measured using the laser Doppler velocimetry (LDV) technique. The LDV data, when taken in combination with flow visualizations, revealed different mixing mechanisms for each velocity ratio, The 3:1 ratio behaved similarly to a single jet, with the structures due to the. Kelvin-Helmholtz instability and the streamwise vortices interacting together to substantially enhance mixing. The 1:1 velocity ratio, which minimizes the Kelvin-Helmholtz instability, relied mainly on the streamwise vortices to also substantially increase mixing. The 1:3 case behaved like a wake flow, with the LDV data showing the streamwise vortices much more confined radially and dissipating quickly, The inner stream, for this case, was greatly influenced bg the outer stream and its interaction with the ambient air.