Objectives The load reduction technology of launcher muzzle air curtain reduces the launch load on an underwater vehicle by injecting air at the launcher muzzle during launching. To accurately simulate the process of a full-scale vehicle exiting the tube under complex environmental conditions through scaled-down experiments, it is necessary to study the similarity criterion governing the engineering-scale tests of this load reduction technology of launcher muzzle air curtain.

Methods Based on the relevant influencing parameters of underwater launching, the π theorem is applied to derive the similarity criteria governing the underwater launch process. At the same time, similarity analysis is conducted for the pressure equalization and exhaust processes of the vehicle, as well as for the air curtain injection process, to establish the similarity criteria of the decompression model. To address the issue that the bubble pressure and bubble range during air curtain injection cannot be simultaneously matched under the similarity criteria of the decompression model, additional similarity criteria for an isobaric model are developed. Finally, comparative experimental tests are performed to analyze the differences between the decompression model and the isobaric model.

Results Compared with the decompression model similarity criterion, the isobaric model similarity criterion can more accurately simulate the process of uniform pressure exhaust and air curtain injection for the vehicle. It better satisfies the similarity requirements of cavity pressures, cavity shape, and bubble range. The scaled testing scheme based on the isobaric model similarity criterion can effectively capture the load characteristics and attitude behavior of the full-scale vehicle under the load reduction technology of launcher muzzle air curtain.

Conclusions The research results provide a reference for simulating complex underwater launch environments.