Open Access

ARTICLE

On the Formation Mechanism and Characteristics of High-Pressure Percussion Pulsed Water Jets

Yong Liu¹, Jianping Wei^2,3

1 State Key Laboratory Cultivation Base for Gas Geology and Gas Control, Henan Polytechnic University, Jiaozuo, China
2 The Collaborative Innovation Center of coal safety production of Henan Province, Jiaozuo 454000, Henan, China
3 Corresponding author

Fluid Dynamics & Materials Processing 2015, 11(3), 221-240. https://doi.org/10.3970/fdmp.2015.011.221

Abstract

Although the socalled percussion-pulsed-water jet technique is currently recognized as an effective means for breaking hard rocks, it can’t be extensively employed due to insufficient systematic research on the related flow-field structure. Considered as one of the rock breaking technologies with the highest potential of development and application, this method is characterized by water hammer effects, a high-frequency impact pressure and high-speed side flows. The typical (impact and extrusion) pistons used for this technique collide several times to form the multi-pulsed jet. Here we analyze these features through a combined experimental-numerical investigation. The number of pulses and kinetic parameters of the jet are studies as a function of the mass of piston, the speed of the impact piston before collision, the diameter of water chamber, the water depth in the chamber and the nozzle diameter. Interestingly, the jet pressure and velocity first increase from zero and then decrease following a non-linear (quadratic) law. As the mass of the extrusion piston is reduced, the number of pulses increases. We also study in detail the typical umbrella-shaped configuration of the pulsed jet by means of a VOF numerical method. We show the existence of a back jet and a front jet transporting fluid away from the central regions under the action of air friction and resistance. With the loss of acceleration, the jet moves backward giving rise to an umbrella structure. The formation of the umbrella shape is observed to improve the degree of convergence. A low-velocity layer is identified at the front of the jet, where the turbulent kinetic energy is relatively high.

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Keywords

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