Jet characteristics from a submerged combustion system

► Gas-liquid case had an order of magnitude lower Strouhal number than gas-gas case. ► Pressure fluctuations in the gas chamber linked with two phase instability. ► Helium-water case had much higher pressure fluctuations than air-water case. ► Elliptical nozzles had lower noise than circular, triangular or square nozzles. ► Examined gas jet instability in shallow and deep underwater propulsion cases.