Optimal Design of Novel Drill Bit to Control Dust in Down-the-Hole Hammer Reverse Circulation Drilling

In pneumatic down-the-hole hammer drilling with reverse circulation, dusty air often escapes from the borehole due to the adverse effects of reverse circulation, which not only pollutes the surrounding environment, but also affects workers' health. In order to address this issue, a new type of drill bit, designed with a swirling generator, has been developed. The computational fluid dynamics code ANSYS Fluent was used to simulate the swirling flow phenomena inside the drill bit, and the simulation results indicate that a stronger swirling flow field can be formed in the drill bit's center passage. This swirling flow has a high entrainment effect, so that negative pressure is generated in the nearest area, which is helpful for improving the reverse circulation effects. Furthermore, a series of experiments were carried out to test the actual performance of the drill bit, and the experimental results exhibit reasonable agreement with the simulation data. The maximum error between the simulated and experimental results is only 9.05%. The mass flow rate of the sucked air increases with an increase in air supply, regardless of whether flushing nozzles are designed for the drill bit. Moreover, the amount of air sucked into the swirling drill bit is greater than that sucked into the annular drill bit under the same conditions; therefore, the swirling drill bit exhibits superior performance.