Investigation of Cuttings Transport in a Reverse Circulation Drill Bit during Direction Drilling Using Two-Phase Flow Simulation.

Effective removal of cuttings from the central channel of the drill tool is critical for directional drilling using pneumatic down-the-hole hammers, yet the flow behavior of cuttings in reverse circulation drill bits remains unclear. This study establishes a validated Computational Fluid Dynamics (CFD) model that quantifies borehole cleaning efficiency through Eulerian-Eulerian two-phase flow simulation, enabling precise optimization of reverse circulation performance and cutting transport capacity under varying structural and operational conditions. The reliability of the simulation results is validated by a series of experiments. The findings reveal that cuttings carrying efficiency is primarily influenced by suction force and the scouring effect of air from flushing nozzles. Reducing the diameter of the flushing or inner suction nozzles improves the reverse circulation. Additionally, increasing the air volume flow rate enhances the cutting transport efficiency, while increases in borehole inclination, penetration rate, particle size, and rotation speed reduce this efficiency. The study also shows that reverse circulation can be improved with an increased inclination angle and air volume flow. These insights provide valuable guidance for optimizing reverse circulation drill bits, improving efficiency, and minimizing environmental impacts during directional drilling.