Propagation of detonation waves crossing the gas-liquid interface is a basic phenomenon worth studying for underwater detonation engines. In this work, the pressure evolution of detonation waves penetrating into water is theoretically and experimentally investigated. The one-dimensional shock wave theory is adopted to solve the pressure-velocity relations of the reflected and transmitted shock wave in different mediums. Experiments under different filling pressure are performed based on a two-phase shock tube system. Theoretical results show that the range of pressure rise ratios between the detonation and transmitted wave is 2.40-2.50. And its trend is determined by the total atoms number of fuel under low filling pressure, but dominated by the ratio of C/H atoms under high filling pressure. Experimental results demonstrate that pressure rise ratios are in good agreement with the theoretical values. There are similar attenuation laws (decay to 50% in 0.3ms) for subsequent pressure development after those two waves. Under the interface effect, the transmitted wave is stretched and the pressure zone becomes wider. The difference of acoustic impedance between two phases leads to wave property changes at the interface and exit. These changes result in the reciprocating cavitation zones and reformed shock waves in the water, greatly influencing the water pressure.

The forward reflection of detonation waves on the solid wall will lead to a high pressure rise. The research systematically introduced the theoretical, numerical, and experimental exploration on the shock propagation characteristics of detonation waves forward impacting on a solid wall in the present work. The one-dimensional shock theory was carried out to solve the pressure rise ratio in this process. The exact solution and its variation law of a positive increase with filling pressure were expressed. One-dimensional simulations based on the space-time conservation element and solution element method were utilized to reveal the pressure decrease and velocity increase laws for the reflected shock wave. The blockage, oscillation, and attenuation phenomena of detonation waves and reflected shock waves under the effect of the tube–wall reflection were demonstrated in two-dimensional works. Experimental results from the detonation tube pressure test system showed a larger amplitude and duration of the reflected shock wave than the detonation wave. Pressure evolution and the formation of pressure plateaus were consistent with the simulation results. In addition, the time required for the pressure plateaus to decay to 0.5 times the Chapman-Jouget (C–J) detonation pressure is relatively constant under different filling conditions.

The detonation-powered underwater engine, with the advantages of high specific impulse, high speed, and simple structure, has very broad application prospects in the field of underwater propulsion, and dual-tube combination is an effective means to improve its propulsion performance. In this work, near-field pressure evolution of shock waves and high-pressure zones between two detonation tubes is numerically studied. The two-fluid model and three-dimensional conservation element and solution element method are adopted to reveal the formation, intersection, and interaction of shock waves. Detonation waves generated by two detonation tubes decouple into shock waves after penetrating into water and form a high-pressure zone near each tube exit. The two leading shock waves intersect with each other in the propagation, creating the second high-pressure zone between two tubes. Then, a propagating forward merged new shock wave covers the two original wave-fronts and maintains higher pressure. Pressure evolution under different tube intervals, ignition delays, and filling conditions is also presented to discuss their influence on the performance of dual-tube detonation. The intensity and directivity of shock waves are found to be sensitive to these factors, complexly affecting the thrust components, which provides a depth understanding of dual-tube combination in the application.