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An underwater detonation tube (DT) experiment is carried out in a water tank to investigate the bubble dynamics and pressure field characteristics of an underwater detonation gas jet. In the experiment, a 0.78 liter DT filled with a 0.29 MPa methane–oxygen mixture (equivalent to 0.85 mg of TNT, trinitrotoluene) is detonated. By means of high-speed photography and pressure field measurements, the jet process is divided into four different stages. The evolution patterns and features of the four stages are characterized according to the morphology of the detonation gas bubble, and the dimensionless parameters of the bubble dynamics are defined and calculated using image post-processing. The transmitted shock wave and pressure pulsations of the bubble oscillations are extracted using a low-pass filter with a cutoff frequency of 1000 Hz. The time intervals between consecutive pressure peaks are compared with the oscillation periods obtained from parameter studies of bubble dynamics. The bubble dynamics generated by the sudden release of detonation products in the first oscillation are found to be similar to those of underwater explosions. An expansion-necking structure is observed, formed by the impulsive release of the remaining detonation gas from the DT. A numerical simulation is conducted under the same filling conditions as the experiment to supplement the experimental results. The experiment demonstrates the feasibility of underwater detonation gas jets, which could provide an alternative means of generating pulsation bubbles.

The detonation engine, which can produce high specific impulse during the underwater detonation process (UDP), has become the forefront of underwater propulsion. In this paper, the thrust mechanism conducted in UDP and the propagation characteristics of the complex pressure waves are numerically studied, and the correlation between those two features is analyzed. The thrust from UDP is generated in a submerged detonation tube (SDT) and driven by the stoichiometric methane-oxygen mixture. The results show that detonation of the pre-filled combustible gas mixture gives rise to complex pressure waves and delivers several force impulses to the SDT. The impulses present different effects on the thrust performance, which is divided into two stages. In the first stage, before the detonation wave collides with the exterior water, the thrust is provided by the persistent back pressure effect of the detonation product. When the detonation wave propagates through the SDT exit and strikes the gas-water interface, a transmitted shock wave and a reflected shock wave are formed, which produce the impulses dominating the second stage. The reflected shock wave eventually impinges on the inner wall, imposing a force impulse on it. The pressure disturbance on the annular wall caused by the transmitted shock wave and subsequent detonation gas jet leads to another two thrust impulses. Finally, a comparison between the thrust of the SDT and its counterpart in air is conducted to characterize the influence of UDP, and the effects of dimensional parameters of the SDT are also investigated.

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