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.
Highlights
This paper focuses on the effects of the helical angle and the area ratio on the reverse circulation effect by using Computational fluid dynamics (CFD) simulations
The influence of the helical angle and area ratio of the swirling drill bit on the effect of reverse circulation were studied by means of CFD simulations, the influence of the ice core’s length on the entrainment ratio during core drilling was analyzed, and a compari‐
The influence of the helical angle and area ratio of the swirling drill bit on the effect of reverse circulation were studied by means of CFD simulations, the influence of the ice core’s length on the entrainment ratio during core drilling was analyzed, and a comparison between the swirling drill bit and a normal drill bit was conducted
Summary
Ice coring technologies play a crucial role in scientific research on the polar region [4,5]. The ice drilling technology is divided into mechanical drilling and thermal drilling. At present, armored cable-suspended electromechanical drills are commonly used in ice core drilling. Because the circulation medium of the drilling tool is drilling fluid, it can leak and pollute the polar environment when working in the snow-firn zone above the ice sheet [6,7,8,9]. In order to solve these problems, scientists propose to apply air reverse circulation drilling technology to polar ice drilling. During air reverse circulation drilling, compressed air enters the annular space in double-wall drill pipes through a dual-channel swivel and goes down. After entering the drill bit, part of the air flow enters the central passage through the ejector device on the upper part of the drill bit to form a high-speed jet, and the other part of the air flow reaches the bottom of the borehole through the flushing nozzles at the bottom of the drill bit, enters the central passage under the entrainment of the high-speed jet
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