Coupling Mechanism Between Triangular Three-Nozzle Rocket-Sled Jet and Ground Effect and Its Layout Effects

To investigate the complex wake field characteristics of multi-motor parallel rocket sleds, this study focuses on analyzing the mechanisms by which horizontal nozzle center distance and impact height influence flow structures and ground effects. By comparing four operating conditions including large spacing (l=7d), small spacing (l=1d), low impact height (h=2d), and high impact height (h=5.5d)，this study systematically reveals the flow field structure, pressure distribution, and thermal erosion behavior on the ground under different configurations. Results indicate：(1) The small-spacing layout induces strong jet interference in the absence of ground effect, resulting in a “multi-peak-slow-recovery” pressure recovery characteristic that significantly delays the flow field relaxation process. (2) The coupling effect between ground effect and interference is dominated by impact height. At low impact height, jet impact induces violent vortex restructuring and fragmentation, forming wall jets with velocities up to 960 m/s. Peak surface temperatures reach 1286.6 K with sustained high temperatures, significantly increasing track ablation risks. In contrast, high impact heights effectively suppress ground effects, leading to a more uniform and stable flow field structure. Peak surface temperatures decrease by approximately 65%, maximum flow velocities reduce by 58%, and ablation risks are significantly mitigated. (3) The rocket skid initial phase (0-8 m) represents the most severe thermal-mechanical loading zone. During this stage, the average acceleration reaches 832.7 m/s², coupled with a prolonged duration per unit distance of 1.84 ms/m. This interaction with transient complex flow fields constitutes the highest risk for orbital ablation. Numerical simulation results closely matched high-speed photography test outcomes in flow field morphology, shock height, and vortex core location, validating the reliability of the established “internal ballistics-external ballistics-flow field” coupled model. This study elucidates the complex flow patterns of a multi-nozzle parallel system under severe constraints, providing crucial theoretical foundations and design parameters for structural layout optimization and thermal protection design in high-acceleration, heavy-load rocket sled test systems.