CFD-Based Parametric Optimization of a Jet-Assisted Reverse-Circulation HDD Reamer for Cuttings Transport in Large-Diameter Pipeline Crossings

Large-diameter horizontal directional drilling (HDD) pipeline crossings often suffer from inadequate hole cleaning during reaming because the enlarged borehole reduces annular velocity and promotes cuttings-bed formation. Cuttings accumulation can increase torque and drag, raise the risk of stuck-pipe incidents, and compromise installation safety. To improve cuttings removal, this study investigates a jet-assisted reverse-circulation HDD reamer using an experimentally benchmarked computational fluid dynamics–discrete phase model (CFD–DPM) workflow. The model focuses on the internal ejector-assisted suction and return-flow process of the reamer. Three k - ε turbulence closures, namely, the standard, RNG, and realizable k - ε models, were benchmarked against experimental pressure-ratio data. The standard k - ε model showed the best overall agreement, with relative errors ranging from 2.5% to 7.1% and an average error of 4.43%, and was therefore selected for subsequent parametric simulations. The results indicate that the nozzle-to-throat distance, throat length, and diffuser angle strongly affect the hydraulic performance of the internal ejector structure. For the present reamer configuration, a nozzle-to-throat distance of l n t = 1.0 − 1.25 d n , a throat-length estimate of l t , opt = ( 3.83 + 2.88 q ) d t , and a diffuser angle of θ d ≈ 5 ° are recommended within the investigated operating range. For cuttings capture, a suction-port diameter of d s = ( 2 − 3 ) d p and N s = 3 – 4 suction ports provide a practical balance between geometric passage capacity and through-port suction velocity. Increasing cuttings size and cuttings volume fraction both reduce the pressure ratio and ejector efficiency, with the influence becoming more pronounced at higher flow-rate ratios. These results provide relative design guidance for improving suction performance and cuttings-transport efficiency in jet-assisted reverse-circulation HDD reamers, while field-scale validation with full annular flow and dense particle interactions remains necessary.