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 from L = 0 mm, H = 0 mm to L = 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 dualgroove spacing L0 increased from 0 to 1.5 mm, the maximum Von Mises stress first rose sharply to a peak, then decreased to approximately 3 MPa at L₀ = 0.25 mm, and remained nearly stable for L₀ > 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%.