Experimental and Numerical Study on Air Flow Behavior for a Novel Retractable Reverse Circulation Drill Bit of Casing-while-Drilling (CwD)

Figure 3

Air circulation in drilling. 1: lower drill bit; 2: casing shoe; 3: flushing nozzles; 4: inner jet nozzles; 5: casing; 6: air hammer; 7: splined sleeve; 8: upper drill bit body; 9: suction channel; 10: spiral slots; 11: borehole wall.

(a) Drilling status

(b) Removal from borehole