Numerical Simulation Study of a Swirling Drill Bit Used for Ice Core Drilling

Abstract

Due to its high mechanical penetration rate and lack of pollution of the environment, air reverse circulation drilling is considered to be a promising method for ice drilling. The air reverse circulation is caused by the combination of the ejector and the flushing nozzles in the drill bit. In this paper, CFD software was used to simulate the influence of the structure of the swirler on the effect of air reverse circulation in the swirling drill bit, and a testing stand was established for the testing of air reverse circulation. The results show that for drill bits without flushing nozzles, the smaller the helical angle is, the larger the entrainment ratio will be, meanwhile the smaller the area ratio is, the larger the entrainment ratio will be. In contrast, for drill bits designed with flushing nozzles, the larger the helical angle is, the larger the entrainment ratio will be, and the larger the area ratio is, the larger the entrainment ratio will be. In addition, the presence of the ice core sharply reduces the effect of air reverse circulation. When the ice core’s height exceeds that of the outlet of the swirler, the reverse circulation effect is slightly improved.

Simulation Study of the Transport Characteristics of the Ice Core in Ice Drilling with Air Reverse Circulation

“…The b-value is always 1.04, independent of the geometric characteristics of the ice core and pipe. According to the similarity principle, it can be considered that when 0.80 ≤ ϕ ≤ 0.92, 1 ≤ λ ≤ 4, 0 ≤ ε ≤ 0.9 in pneumatic conveying, the maximum velocity of the cylindrical object satisfies Equation (7). The structural form of this equation is similar to the equation of capsule velocity in hydraulic transportation.…”

“…Drilled ice cores and cuttings are carried to the ice core barrel and ice cutting chamber by a special low-temperature drilling fluid that circulates locally at the bottom of the hole. After filling the ice core barrel (generally 2~4 m) and ice cutting chamber in the drills, the drills must be lifted to the surface for treatment before reinserting into the borehole for subsequent drilling [7]. The drills' single drilling depth is short, and the drills must be continuously tripped in and out of the borehole, resulting in a low drilling rate of penetration and, finally, efficiency.…”

“…core barrel (generally 2~4 m) and ice cutting chamber in the drills, the drills must be lifted to the surface for treatment before reinserting into the borehole for subsequent drilling [7]. The drills' single drilling depth is short, and the drills must be continuously tripped in and out of the borehole, resulting in a low drilling rate of penetration and, finally, efficiency.…”