A large proportion of minable coal seams in China belong to low-permeability soft coal seams. Such coal seams suffer serious coal and gas outburst hazards and endure a high incidence of major disasters in coal mines. The adoption of the high-pressure water jet (HPWJ) hydraulic flushing cavity can effectively promote the gas drainage efficiency and volume and eliminate the hidden danger of gas disasters. Nevertheless, the shape and impact pressure of rotating HPWJ are rarely researched. In this study, on the basis of the numerical simulation, the axial and radial stress distributions of HPWJ and the energy-gathering effect of a conical-cylindrical combined nozzle were analyzed. It is concluded that the submerged condition will accelerate the attenuation of jet velocity and reduce the impact strength of the jet. The jet diffusion angle grows with the increases in the nozzle diameter and water pressure, and 24° is the optimal contraction angle. Finally, the influences of factors such as the rotation speed on the shape and impact pressure of HPWJ were explored, and the results show that the rotation speed should be controlled within 90 r/min. The research findings lay the foundation of the study on the mechanism of coal crushing by HPWJ and provide technical support for the research and development of drilling and flushing integrated equipment.

中文翻译：

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水力冲腔技术中高压水射流形状及冲击压力分析

我国可采煤层很大一部分属于低渗透性软煤层。此类煤层煤、瓦斯突出危害严重，煤矿重大灾害发生率高。采用高压水射流（HPWJ）水力冲洗腔，可有效提升瓦斯抽采效率和容积，消除瓦斯灾害隐患。然而，很少研究旋转HPWJ的形状和冲击压力。本研究在数值模拟的基础上，分析了HPWJ的轴向和径向应力分布以及锥筒组合喷嘴的聚能效果。得出的结论是，淹没条件会加速射流速度的衰减，降低射流的冲击强度。射流扩散角随着喷嘴直径和水压的增加而增大，24°为最佳收缩角。最后，探讨了转速等因素对HPWJ的形状和冲击压力的影响，结果表明转速应控制在90 r/min以内。该研究成果为HPWJ碎煤机理研究奠定了基础，为钻冲一体化设备的研发提供了技术支持。