To improve the cuttings transport efficiency in large-diameter HDD reaming (600mm and larger), a new type of reverse-circulation reamer was innovatively designed based upon the jet pump design theory and an experimental system was then established to investigate the effects of operating conditions on its non-cavitating and cavitating performance. Computational fluid dynamics (CFD) was also used to simulate the internal flow field of the proposed reamer and the reamer’s structure parameters including the nozzle-to-throat space, throat length, and diffuser angle were thereby optimized. The results indicate the reamer’s non-cavitating performance curve can be approximated by a straight line with an intercept of 0.44 and a slope of 0.26 and its efficiency peaks at 0.242; neither primary flow rate Qn nor suction pressure Ps makes an evident difference to the reamer’s non-cavitating performance, but increasing Qn or decreasing Ps undermines the reamer’s anti-cavitation capability; and rotary speed n does not exert influence on its non-cavitating or cavitating performance. The optimal nozzle-to-throat space and diffuser angle equals 1.6 times the nozzle diameter and 5º respectively, while the optimal throat length is found to be 3.83+2.88q times the throat diameter.
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