Differences in Predicting Hollow Structures of Water‐Assisted Injection‐Molded Rectangular Tubes Between Laminar and SST k – ω Turbulence Models Under Various Water‐Injection Pressures

ABSTRACT To investigate the influence of flow models on hollow structure prediction in water‐assisted injection molding (WAIM), three‐dimensional numerical simulations were performed using the finite volume method with the laminar model and the shear stress transport (SST) k – ω turbulence model. The hollow profile evolution, the hollow ratio distribution, and the coefficient of variation ( CV ) predicted at water‐injection pressures of 6, 8, and 10 MPa were validated against experimental measurements. The results indicate that both flow models successfully captured the trends of increasing hollow ratio and decreasing CV with increasing water‐injection pressure. Nevertheless, the SST k – ω turbulence model yielded hollow profile evolution and hollow ratio distribution that agreed more closely with the experimental measurements, owing to its ability to capture local turbulent and interfacial fluctuations associated with high‐Reynolds‐number water penetration. In contrast, by neglecting turbulent effects, the laminar model produced pronounced conical distortion in the hollow profiles at the rear cross‐sections and unrealistically smooth hollow ratio distributions at high water‐injection pressures. Although the laminar model yielded CV values that were numerically closer to the experimental results, this agreement was largely an artifact of its smoother hollow ratio distributions combined with the inability of CV to capture local distortions in hollow profile. Overall, the SST k – ω turbulence model provided a more realistic representation of the flow field and superior capability in predicting hollow structure evolution during WAIM.