Reverse circulation down-the-hole (RC-DTH) air hammers have been widely used in construction and mining activities owing to their high drilling efficiency and good dust control performance. This paper presents a computational fluid dynamics (CFD) approach with the dynamic mesh method for evaluating the performance of RC-DTH air hammers. Nine stages of operating conditions of the RC-DTH air hammer are described herein to better understand the operating mechanism of the RC-DTH air hammer. Dynamic layering, sliding interfaces, as well as user-defined functions were employed to update the mesh in dynamic mesh modelling. The influences of rebound coefficient, input air pressure, and piston mass on the performance of RC-DTH air hammers were studied. It was found that increasing the rebound coefficient and input air pressure can improve the impact performance of RC-DTH air hammers, whereas increasing input air pressure can reduce energy efficiency and increase energy consumption. In addition, simulation results indicate that increasing the input air pressure may increase the stroke of the piston; the piston mass should be optimally selected to match the designed geometric parameters to avoid a significant drop in performance. The CFD approach with the dynamic mesh method shows superiority in evaluating the performance of RC-DTH air hammers.

Reverse circulation down‐the‐hole (RC‐DTH) air hammer drilling is a fast and cost‐effective method for hard rock drilling. As the air RC drill bit is the heart for RC‐DTH air hammer drilling system to form the reverse circulation, a large‐diameter RC drill bit was innovatively designed and numerically optimized with respect to the suction ability. Results show that increasing the suction‐nozzle elevation angle and deflection angle can improve the drill bit suction ability. The drill bit performance reaches its optimal state when the air flow rate was about 1.205 kg/s, thereafter it exhibits a reverse variation trend with the increase in air mass flow rate. The optimum diameter of the suction nozzles is 20 mm for the drill bit studied in this work. The RC drill bit with outer diameter of 665 mm and RC‐DTH air hammer with outer diameter of 400 mm were manufactured and a field trial was conducted. Field test results show that the penetration rate using the RC‐DTH air hammer drilling method is more than twice the conventional rotary drilling method. This drilling approach poses a great potential for the large‐diameter hard rock drilling applied in the upper portions of a well bore above the potential producing reservoir formation for land oil and gas drilling, geothermal drilling and relevant field drilling operations.