Flow structures of gaseous jets injected into water for underwater propulsion

Abstract

Gaseous jets injected into water are typically found in underwater propulsion, and the flow is essentially unsteady and turbulent. Additionally, the high water-to-gas density ratio can result in complicated flow structures; hence measuring the flow structures numerically and experimentally remains a challenge. To investigate the performance of the underwater propulsion, this paper uses detailed NavierStokes flow computations to elucidate the gas-water interactions under the framework of the volume of fluid (VOF) model. Furthermore, these computations take the fluid compressibility, viscosity, and energy transfer into consideration. This paper compares the numerical results and experimental data, showing that phenomena including expansion, bulge, necking/breaking, and back-attack are highlighted in the jet process. The resulting analysis indicates that the pressure difference on the rear and front surfaces of the propulsion system can generate an additional thrust. The strong and oscillatory thrust of the underwater propulsion system is caused by the intermittent pulses of the back pressure and the nozzle exit pressure. As a result, the total thrust in underwater propulsion is not only determined by the nozzle geometry but also by the flow structures and associated pressure distributions.

The Evolution of Interfaces for Underwater Supersonic Gas Jets

“…All of the simulations were modeled using the commercial CFD (Computational Fluid Dynamics) code, ANSYS-Fluent. The VOF multi-phase model is used to track the change of gas-liquid interface, and this model has been validated in getting the fraction of gas in underwater gaseous jets [10,15,19]. The two-dimensional axisymmetric geometric model with the same size of water vessel is established for simulation, and the pressure-velocity coupling SIMPLE algorithm is used to solve the discrete equations.…”

“…Loth et al [9] found that the same shock structures in the wake of a sonic jet underwater. Wang et al [10,11], Shi et al [12,13], and Tang et al [14,15] found that expansion, necking, and back-attack are fundamental phenomena in underwater gas jets. Tang et al [16,17] considered phase transitions and the buoyancy effect of gaseous jets for underwater propulsion systems through numerical simulation, and found that the thrust shows different orders of frequency attributed to the oscillation in wake.…”

Estimation of the radioactive aerosols capture in accidental sequences of nuclear power plants

“…A development of "Back-Attack phenomenon" in supersonic gaseous jets was made by Tang et al [Tang, 2011]. The converging-diverging Laval nozzles are used in Tang's article.…”

“…Observations of Dai et al [Dai, 2006] have shown that the injection process of high-speed gaseous jets in still water can induce large pressure pulsations upstream of the nozzle exit, and that the shock-cell structures in the over-and under-expanded jets can lead to strong changes in the hydrodynamic pressure. Shi et al [Shi, 2010] have shown that the injection of supersonic gaseous jets into water causes large flow oscillation, which can be related to shock waves reflecting in the gas phase and, complementarily, Tang et al [2011] has observed the back-attack phenomenon.…”

“…Only a reduced number of previous investigations have been focused in the exploration of the physics of these processes. From them can be highlighted, among others, the works of Loth and Faeth [Loth, 1989;Loth 1990], Gamble et al [Gamble, 2001], Gulawani et al [Gulawani, 2007], Someya et al [Someya, 2011], Tang et al [Tang, 2011], Weiland et al [2013], Roger et al [Roger, 2014], etcetera.…”