Erosion Characteristics of a Novel Spherical Swivel in Air Drilling: Insights from Gas–Solid Two-Phase Flow Simulation

In air reverse circulation drilling using double-wall drill pipes, the elbow swivel is prone to failure and leakage under the high-speed impact of rock cuttings. To address these challenges, in this study a novel spherical swivel was proposed. A coupled CFD-DPM method was employed within Euler–Lagrange framework and Huser–Kvernvold erosion model to investigate the erosion behavior and the mechanism of rock cuttings in the spherical swivel. Simulation results reveal that, in contrast to the severe erosion of the traditional elbow swivel caused by repeated collisions of rock cuttings in local areas, the erosion in the spherical swivel is dominated by the initial impact of rock cuttings. Within the spherical chamber, rock cuttings are effectively dispersed without significant superposition of secondary impacts. The maximum erosion rate of the spherical swivel is approximately 42% lower than that of the conventional elbow swivel. An increase in the chamber diameter of the spherical swivel can further reduce erosion by enhancing particle kinetic energy dissipation and minimizing impact superposition, while the angle between the inlet and outlet pipes shows a negligible influence on the erosion characteristics. Furthermore, a higher drilling rate substantially intensifies erosion due to the increased generation of rock cuttings per unit time. The greater cuttings velocities correspond to the higher kinetic energy, and, consequently, more severe erosion. Given that the size of rock cuttings is inherently small, variations in their size have a limited effect on the erosion behavior. The findings provide crucial insights for improving the drilling efficiency and operational safety in air reverse-circulation drilling systems.