Key Takeaways & Executive Findings
- •• AFESOPWs exhibit an additional self-priming frequency that synergizes with the second high-amplitude frequency band, producing larger pressure amplitudes. • Three high-amplitude frequency bands in waterjet pressure correspond to plunger pump excitation, shearing layer vortex, and bubble collapse. • Self-priming of annulus fluid enhances cavitation, with cavitation cloud shedding frequency linearly related to cavitation number. • Modulating pressure oscillation and cavitation shedding frequencies can improve peak pressure and cavitation erosion effectiveness.
Abstract
Under submerged conditions, compared with traditional self-excited oscillating pulsed waterjets (SOPWs), annular fluid-enhanced self-excited oscillating pulsed waterjets (AFESOPWs) exhibit a higher surge pressure through self-priming. However, their pressure frequency and cavitation characteristics remain unclear, resulting in an inability to fully utilize resonance and cavitation erosion to break coal and rock. In this study, high-frequency pressure testing, high-speed photography, and large eddy simulation (LES) are used to investigate the distribution of the pressure frequency band, evolution law of the cavitation cloud, and its regulation mechanism of a continuous waterjet, SOPW, and AFESOPW. The results indicated that the excitation of the plunger pump, shearing layer vortex, and bubble collapse corresponded to the three high-amplitude frequency bands of the waterjet pressure. AFESOPWs have an additional self-priming frequency that can produce a larger amplitude under a synergistic effect with the second high-amplitude frequency band. A better cavitation effect was produced after self-priming the annulus fluid, and the shedding frequency of the cavitation clouds of the three types of waterjets was linearly related to the cavitation number. The peak pressure of the waterjet and cavitation erosion effect can be improved by modulating the waterjet pressure oscillation frequency and cavitation shedding frequency.
1. Introduction
Waterjets are recognized for their cleanliness and efficiency, making them widely applicable in various fields, including mining, tunnelling, deep sea mineral extraction, oil-gas drilling, exploration of geothermal reservoirs. However, under submerged conditions, the use of a waterjet for rock breaking or assisting in rock breaking remains a key technological challenge [1]. In contrast, pulsed water waterjets can produce discrete water bombs with large pressure oscillation, effectively mitigating the effects of pressure retention and the increased resistance caused by the water cushion.
Previous studies have shown that, when two self-priming holes are set at suitable positions on both sides of a Helmholtz oscillation cavity, the fluid in the annular space outside the cavity is sucked into the cavity under the action of high-speed waterjet entrainment and pressure gradient inside and outside the cavity, forming an annular fluid-enhanced self-excited oscillation pulsed waterjet (AFESOPW) [2,3]. Compared with traditional self-excited oscillating pulsed waterjets (SOPWs), AFESOPWs have a larger flow rate and higher surge pressure. When drilling in coal seam or rock stratum, coal and rock debris can be absorbed to form an abrasive waterjet, which further enhances the crushing effect of coal and rock. It also has broad application prospects in deep mining and deep-sea mining [4,5].
The resonance effect can be used to enhance the efficiency of coal and rock fragmentation. Li et al. [6] discovered based on vibration principles that when the excitation frequency matches the natural frequency of the rock, the vibration displacement of the rock increases significantly, leading to improved fragmentation.
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Haojie Jia, Yanwei Liu, Weiqin Zuo, Hongkai Han, Ping Chang, Mohammad Waqar Ali Asad, Guozhong Hu, Jian Miao, Hani S. Mitri (2025). Multi-frequency formation mechanism and modulation strategy of self-priming enhanced submerged pulsed waterjet. SinoTechIntel Verified Research. https://doi.org/10.1016/j.ijmst.2025.01.002
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Frequently Asked Questions
What is an AFESOPW and how does it differ from a traditional SOPW?
An AFESOPW (annular fluid-enhanced self-excited oscillating pulsed waterjet) is a type of pulsed waterjet that uses self-priming holes to draw annular fluid into the oscillation cavity, resulting in a larger flow rate and higher surge pressure compared to traditional SOPWs.
What are the three high-amplitude frequency bands in waterjet pressure?
The three high-amplitude frequency bands correspond to the excitation of the plunger pump, the shearing layer vortex, and bubble collapse.
How does self-priming affect cavitation in submerged waterjets?
Self-priming of the annulus fluid enhances the cavitation effect, and the shedding frequency of cavitation clouds is linearly related to the cavitation number.
What is the practical significance of modulating pressure oscillation frequency?
Modulating the pressure oscillation frequency and cavitation shedding frequency can improve the peak pressure and cavitation erosion effect, which is beneficial for breaking coal and rock.
What methods were used to investigate the waterjet characteristics?
The study employed high-frequency pressure testing, high-speed photography, and large eddy simulation (LES) to analyze pressure frequency distribution, cavitation cloud evolution, and regulation mechanisms.
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