Study on the effect of gas injection hole radius on mixing and combustion in solid propellant ducted rockets based on total pressure distribution

Combustion efficiency is a key performance indicator for the afterburner of solid propellant ducted rockets. However, insufficient mixing between gas and air often limits further performance improvement. To address this challenge, this study investigates a series of gas injection devices with different injection hole radii and systematically analyzes the effects of hole size on mixing and combustion through numerical simulations. A performance evaluation metric called total pressure non-uniformity is also proposed. This indicator is both reliable and experimentally accessible, and it is used to characterize the spatial uniformity of gas distribution and to predict mixing and combustion efficiency. The accuracy of the simulated total pressure distribution is validated through a ground direct-connected cold flow experiment, with grid independence confirmed. The results indicate that total pressure non-uniformity has a strong negative correlation with both gas-air contact area and combustion efficiency, confirming its effectiveness as a predictive performance indicator. As the injection hole radius decreases, mixing and combustion performance initially improve and then deteriorate. An optimal radius of 4.9 mm reduces total pressure non-uniformity by 22.42 % and increases combustion efficiency by 50.96 % compared to the 10 mm case. This study provides a practical method for predicting mixing performance and optimizing injection structures. It also offers valuable guidance for the development of future mixing enhancement strategies.