Computational fluid dynamics-based flow field simulation and optimization of negative-pressure stone removal: stone size, position, and sheath geometry.

To investigate the flow field characteristics and optimize negative-pressure stone removal strategies using computational fluid dynamics (CFD). A three-dimensional CFD model integrating the UAS, flexible ureteroscope, urinary tract, and spherical stone fragments (1–3 mm) was developed. The low-Reynolds-number *k-ε* turbulence model was applied to simulate the steady, incompressible flow under varying negative pressures. Stone size, position, and sheath parameters significantly affected removal efficiency. 1 mm stones achieved a peak suction force of 0.54 N at 5 mm from the scope tip; 2 mm stones reached 1.68 N at 45 mm, with proximal 1–2 mm fragments experiencing repulsion. 3 mm stones generated the highest force (6.6 N) at 15 mm but showed “jumping” instability due to turbulence. Vortex shedding and low-pressure zones downstream of stones enhanced mobility. The 12/14Fr sheath balanced clearance efficiency and safety. This study revealed that stone size, distance from the scope tip and UAS geometry synergistically regulate clearance efficiency. The identification of a "high-efficiency clearance region" (5–15 mm) and optimal 12/14Fr UAS configuration provides actionable insights for clinical practice, while the proposed optimization framework offers a theoretical basis for next-generation UAS design and standardized negative-pressure stone retrieval protocols.