Liquid/gas coaxial jets, also known as air-blast atomizers, are commonly used in propulsion and energy applications that require the development of a spray. A number of different phenomena are present in this flow, including shear layer and wake instabilities, surface tension, and turbulence at the jet exit. These mechanisms compete with one another to govern the flow development. Recent studies have shown that high Weber number coaxial jets are governed by the shear layer instability, and have dimensionless characteristic frequencies similar to single phase jets. The objective of this research is to explore the robustness of the shear layer mechanism across a wide range of Weber numbers and jet geometries. An experimental study was conducted using a water/air fluid combination across the low to moderate Weber number regimes. High-speed imaging and proper orthogonal decomposition were used to elucidate the spatial and temporal structure of the flow. Convection velocities were also measured using streak imaging. Overall the convection velocity is reasonably estimated using the shear layer theory model, although some deviations were observed. Frequencies including the breakup frequency as well as asymmetric modes were observed. Dimensionless frequencies were found exhibit variation with Weber number.
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