The underwater muzzle flow field formed by the double‐tube launch will interfere with each other, resulting in large changes in the characteristic parameters of the flow field and shock wave morphology. Therefore, the numerical model of three‐dimensional unsteady multiphase flow for underwater gun‐sealed launching was established. Meanwhile, an experimental platform for the underwater sealed launch was built and the rationality of the model was verified. The interior ballistic process compiled by UDF was coupled with the dynamic mesh technology, and the VOF multiphase flow model integrated with the Schnerr‐Sauer cavitation model was chosen to numerically calculate the muzzle flow field of the 30 mm underwater gun double‐tube parallel launch, and the numerical results were compared to those of the single‐tube launch. The results show that the gas is expelled from the muzzle and rapidly expands to form a gas cavity, and the “necking” phenomenon of the gas cavity occurs at 0.2 ms, while the Mach disk structure has formed. Due to the mutual interference between the flow fields formed by each tube, the diameters of the Mach disk are slightly different, and the flow field structure has a certain asymmetry in the evolution process. The core area of the shock wave is bowl‐shaped of the single‐tube launch, while it is not completely filled of the double‐tube launch. Within 0.5 ms, the diameter of the Mach disk increases monotonously when the single‐tube is launched, while it first increases and then decays by a double‐tube.

In the present study, a visual experimental system was built to explore the multiphase hydrodynamic features in the underwater launching process. The whole processes of gas-curtain generation produced by multichannel jet convergence, gas-curtain expansion, and projectile movement were captured using direct photography. The experimental results show that as the area of a single groove grows from 6.25 mm2 to 11.25 mm2, the gas-curtain displacement grows by 47.5%, and the projectile’s speed reduces by 34.1%. The expansion of the gas curtain can be aided by 36.0% by increasing the number of sidewall grooves within a specified range (4 to 8), but the vehicle’s speed is reduced by 53.8%. While increasing the maximum injection pressure from 9.9 MPa to 18.2 MPa, the gas curtain’s draining capability is improved by 29.6%, and the projectile speed increment diminishes (only 10.0%) as the amount of gas flowing into the front of the projectile grows. The impact of jet parameters on gas-curtain displacement and projectile speed is revealed in this study, which is of utmost significance to the parameter-matching design of underwater low-resistance launchers.

The gas-curtain launch is designed to address the shortcomings of conventional underwater launchers, such as poor dependability and low muzzle velocity. In this paper, the influence of jet structures on the propulsion performance and internal flow field of an underwater gas-curtain launcher is investigated. To conduct the experiment on a small-aperture underwater launcher, three projectiles with different jet structures were designed. The experimental results show that a projectile with a central nozzle is more conducive to gas-curtain formation than one with four sidewall grooves. Additionally, the central nozzle can reduce launch resistance and improve propulsion performance more effectively. Furthermore, increasing the diameter of the central nozzle aids in gas-curtain formation and propulsion performance. Following the experiment, a numerical model of the internal flow field for gas-curtain launch is built in order to develop numerical simulations under three jet structures. The calculation results show that the three gas-curtain projectiles can likewise acquire good propulsion performance. Different jet structures have significant impacts on the launching resistance of a gas-curtain launcher, thereby affecting its propulsion performance. The launch resistance is lower when the central nozzle jet structure is utilized; however, the muzzle velocity is also lower because more gas is consumed for drag reduction and the projectile force area is smaller. This study reveals the effect of jet structure on the propulsion performance and flow field evolution of a gas-curtain launcher.

To decrease the launching resistance of underwater guns, a new gas-curtain formation method is proposed based on the gas-curtain launching principle, which is setting up several rectangular grooves on the internal wall of the barrel to guide the gas flow to the front of the projectile and form a gas curtain. A three-dimensional unsteady two-phase flow model of the drainage is established. The formation and drainage characteristics of the gas curtain are studied under the different number of grooves with a constant injection area and 10 MPa injection pressure. The results indicate that the circumferential and radial converging effects of multi-gas jets are enhanced, but the axial expansion is enhanced first and then weakened when the number of grooves increases from 4 to 12. The vortex scale in the Taylor cavity increases with the increase in the number of grooves, but the distance moving downstream is shortened. The gas volume fraction in the tube increases with the increase in the number of grooves. However, the drainage efficiency of the gas curtain on the warhead increases first and then decreases with the increase in the number of grooves, while the change of the gas efficiency–cost ratio is just the opposite.

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