Abstract: To investigate the influence of geometric parameters and velocity ratio on the impingement performance of coaxial water-water jets under low-pressure conditions, nine distinct coaxial nozzles are designed using orthogonal experimental design method. Subsequently, high-speed photography experiments are conducted to analyse the water film formed by the coaxial jet impinging on a flat plate, and jet impact force experiments are also performed. A VOF-CSF coupled model is employed to simulate the water film, elucidating the fundamental reasons for the improved impingement performance of the optimized nozzle. The results show that, at a total flow rate of 6 L/min, the relative position of the inner and outer nozzles has a significant impact on the jet impact force, while inner nozzle thickness has minimal effect. Mean impact force values generally decrease with increasing velocity ratio for most nozzle configurations. Furthermore, under a constant inner jet flow rate, experimental and simulation results for the water film radius show good agreement, and numerous bubbles are observed within the film. Additionally, the flow turbulence within the film exhibits an increase followed by a decrease as the velocity ratio rises. The comparison before and after nozzle optimization demonstrates that the coaxial jets share similar properties at the same velocity ratio. However, the optimized nozzle model features improved jet focusing, which better enables the transformation of kinetic energy into pressure energy. These results provide valuable guidance for the optimization of low-pressure coaxial water jet design and industrial applications.

Key words: coaxial jet, impinging performance, impact force test, water film, numerical simulation