Methodology and performance of annular fluid enhanced self-excited oscillation in pulsed submerged waterjet for coal mine engineering

Submerged waterjets often yield low coal-breaking efficiency and have limited permeability. This study introduced a novel approach to enhance submerged waterjets by harnessing the annular fluid hydraulic energy of a borehole. A new waterjet modulator was developed using large eddy simulation (LES) combined with the response surface method (RSM). The reliability of the method was verified by submerged waterjet high-frequency pulsation pressure test experiments. The results indicated that the pulsation amplitude of the annular fluid enhanced self-excited oscillation pulsed waterjet (AFESOPW) was 330.05%, 45.17%, and 32.56% higher than those of the continuous waterjet, self-excited oscillation pulsed waterjet (SOPW), and pre-optimized waterjet, respectively. Additionally, the pulsating pressure peak increased by 42.84%, 19.60%, and 25.81%, respectively. Under the submerged condition, the outlet pulsating pressure peak of the AFESOPW was 1.32–1.58 times the inlet pressure. The self-priming annular fluid weakened the hinderance of the submerged environmental pressure and enhanced the waterjet pulsation effect. [Display omitted] •A novel approach to enhance the submerged waterjet was proposed.•The mechanism of self-priming pressurization was revealed.•A new waterjet modulator optimization method was formed.•A new submerged waterjet pulsating pressure test system was developed.