An investigation of gas jets submerged in water

The effects of the ambient-fluid on a compressible gas jet are not well characterized when the ambient fluid is significantly denser than the jet gas. This work uses computational fluid dynamics (CFD) to address the influence of exterior-fluid density for both over- and under-expanded jets. The CFD model uses a turbulence-resolving, multiphase-compressible-flow formulation to: (1) examine the flow structure in this interaction and (2) characterize the observed flow patterns. The main physical finding, which is consistent with previous observations, is that instabilities develop more rapidly at the gas-liquid interface with increased ambient-fluid density. Such instabilities lead to other trends and, with increased density, the model predicts shorter Mach penetration, faster return to ambient pressure, elevated turbulence intensities, and localized liquid jets that attack the gas-jet exit nozzle. Characterizing the results indicates that the main interaction is driven by an explosive mixing-layer growth due to what appear to be Kelvin-Helmholtz instabilities. This amplifies the mixing layer into the jet, while creating an even faster bubble mixing layer that penetrates radially into the ambient fluid. These characteristics are quantified with respect to the ambient-fluid density, providing trends that may be useful for future modeling.