Blast wave induced flow and coaxial liquid jet interaction at the open end of a shock tube

Liquid interfaces interacting with high-speed gas (air) flows are prevalent in both natural and practical settings, resulting in unstable interfacial waves and atomization. This study investigates the flow field created by blast waves or unsteady shock waves at the shock tube exit and its interaction with a liquid jet, demonstrating primary atomization, which is important for efficient injection in combustors, engines, and high-throughput atomizers. A miniature shock tube using the wire-explosion method is used to generate blast waves, enabling a wide range of shock Mach numbers (1.1-1.8). The blast exiting the shock tube diffracts at the inner tube lip, causing the induced flow to roll up to form a compressible vortex ring with a trailing jet. A coaxial metal tube through this rectangular shock tube cavity with its opening just outside the tube exit is employed to maintain a liquid jet that interacts with this decaying flow field, depicting rich interfacial dynamics. The unstable waves of short wavelength are created on the fluid interface which then soon depicts a complex wave structure with wave breaking leading to a cascade of sheets, ligaments, and droplets. This is due to the significant shear generated by the early high-speed airflow, which subsequently decays, and waves with longer wavelengths grow and become more evident in the later stages, leading to a fishbone morphology.