An analysis of flow structures of underwater supersonic gas jets: a numerical study

The present work is focused on the numerical analysis of the flow structures of high-speed underwater air jets. In an earlier work (Jana et al., J. Fluids Eng. 144(11):111208, 2022), the authors presented an analysis of the unsteady behavior of different flow variables of the jets. The present work is further extended to analyze the temporal evolution of the flow structures of different jet regions. The numerical simulations are conducted with the unsteady Reynolds-averaged Navier–Stokes equations with a homogeneous mixture model. The previous work rendered the effect of pressure ratio (the ratio of nozzle exit pressure to back pressure) on the behavior of the jet flow. In the present analysis, jet exit Mach number is also considered as another operating parameter. The results for three pressure ratios, 0.8, 1, and 1.2, and two exit Mach numbers, 2 and 3, are presented. Temporal behavior of the three major regions, namely, the core, shear layer, and mixing layer of the jet due to its interaction with surrounding water, is discussed. The flow physics of shock and expansion waves in the core region is analyzed, and the effects of the underwater ambience on the structures of shock waves are also explained. Various phenomena, such as necking, back-attack, and expansion, are also visualized and explained from the simulated flow variables. Given the limitations of experimental flow visualizations, these analyses aid to understand the major flow behavior of supersonic underwater jets.