With the evolution of efficient gas energy utilization technologies, nozzle-based rear ejection has emerged as a promising approach for recoil reduction in launch systems. This paper systematically investigates the influence of nozzle geometric parameters on the nozzle gas flow field and the recoil reduction performance of the gun through numerical simulation. First, a one-dimensional two-phase flow internal ballistics model for a gun equipped with a rear-ejecting nozzle is developed, along with theoretical methods for calculating the thrust and recoil metrics. Based on this, the unsteady flow field of the nozzle is simulated using a two-dimensional axisymmetric computational fluid dynamics model, employing the gas pressure at the vent obtained from internal ballistic calculation as inlet boundary condition. Pressure tests and flow field visualization experiments validate the accuracy of the simulations. By analyzing the nozzle flow field characteristics under various geometric parameters, the effects of expansion angle, cone length, cylindrical length, and vent position are quantified. Results indicate that recoil reduction efficiency individually peaks at a 5° expansion angle or a 126 mm cone length, reaching 55.7%. Both maximum thrust and recoil reduction efficiency are negatively correlated with cylindrical length and vent position. Furthermore, sensitivity analysis based on orthogonal design reveals that cone length and cylindrical length are the dominant factors determining maximum thrust and recoil reduction efficiency, respectively. From a fluid dynamics perspective, this study provides an effective analytical framework and valuable design guidance for optimizing nozzle configurations to enhance recoil reduction performance.
Xu et al. (Sun,) studied this question.