Effect of piston groove structure on the fluid dynamics of needle-free jet injectors

Compared with conventional needle-based injections, needle-free injections offer several advantages, including ease of operation and elimination of accidental needlestick injury. To investigate the influence of piston structure on the performance of a needle-free injection system, this study combined experiments with fluid-structure interaction numerical simulations to systematically examine the effects of groove length (L), groove height (H), and the spacing (L₀) between the two grooves on jet performance and piston stress. The results showed that during the initial stage of needle-free injection, both the stagnation pressure and jet velocity exhibited pronounced oscillatory behavior, and the driving structure played a significant role in modulating this oscillation pattern. For the single-groove piston, as the groove volume increased fromL= 0 mm,H= 0 mm toL= 3 mm,H= 0.13 mm, the peak stagnation pressure increased by 22.3%, whereas the maximum von Mises stress in the piston rose from 0.53 MPa to 7.21 MPa. Based on the optimal single-groove configuration, the groove was further divided into a dual-groove structure with identical groove length and height. The results indicated that, as the dual-groove spacingL₀increased from 0 to 1.5 mm, the maximum von Mises stress first rose sharply to a peak, then decreased to approximately 3 MPa atL₀= 0.25 mm, and remained nearly stable forL₀> 0.25 mm. Meanwhile, the peak stagnation pressure gradually decreased with increasing groove spacing. Considering the combined variation in peak stagnation pressure and structural stress,L₀= 0.25 mm was identified as the optimal groove spacing. Compared with the optimal single-groove structure, the corresponding dual-groove configuration resulted in a reduction of less than 1% in peak stagnation pressure, while reducing the maximum von Mises stress by 58.4%.