| Self-excited oscillation pulsed jet is an important branch of new water jettechnology, which has many advantages including high energy utilization rate, simplestructure, low cost and so on. As a result, the potential value is very considerable in thefields of coal mining, drilling, cutting, cleaning and surface treatment and so on. But thecomplicated rock breaking mechanism under self-excited oscillation pulsed jet is hard tobe displayed and detected intuitively. Hence, it is particularly important to study therock breaking characteristics of self-excited oscillation pulsed jet comprehensively andthoroughly. Theoretical analysis is combined with numerical simulation method to doexperiments of numerical simulations, as a result, the damage properties of rock underself-excited oscillation pulsed jet and the influence of the key parameters of jet on rockfragmentation efficiency has been researched systematically, and the main conclusionsare as follows:①Combing non-linear dynamics with finite element method to establish a modelof rock breaking under self-excited oscillation pulsed jet. And the result of numericalsimulation is compared with experimental result under the same condition to validatethe model.②The evolution rule of rock damage field under self-excited oscillation pulsed jethas been thoroughly studied. The results show that the development of the rock damagefield along the radial jet begins to stabilize soon and will not be affected by pulseamplitude and pulse frequency basically, meanwhile, the local effect is the main feature.On the contrary, the rock damage field expands rapidly along the jet axis, and thegreater the pulse amplitude, the severer the damage evolution. Besides, the increase ofthe pulse frequency also aggravates the damage evolution along the jet axis, but there isa optimal value. Meanwhile, the stress wave effect occurring in the process of rockfragmentation plays a very important role in aggravating the damage evolution andfailure of microstructure inside the rock.③The process of self-excited oscillation pulsed jet impacting rock under differentpulse amplitude has been simulated. And the results show that the erosion depth hassuccessively undergone rapid growth phase and gradual growth phase, while the erosionaperture basically remains unchanged, and the change rule of different kinds of rock isthe same. But different kinds of rock have different growth rate of erosion depth, the growth rate of coal rock is the largest, while the growth rate of sandstone is the smallest.Besides, the growth of the erosion depth is mainly attributed to the initial phase.④The process of self-excited oscillation pulsed jet impacting rock under differentpulse frequency has been simulated. The results show that with the increase of pulsefrequency, the erosion depth decreases after the first increase, while the erosion aperturebasically remains unchanged, and, the lower the strength of rock, the bigger the peakvalue of erosion depth. Meanwhile, the optimal pulse frequency of coal rock, shale andsandstone are2.5kHz,3kHz and2kHz, respectively.⑤The rock fragmentation efficiency under self-excited oscillation pulsed jet hasbeen quantitatively characterized. The results show that, compared with continuous jet,the coal rock fragmentation efficiency increases48.7%when the pulse amplitude is250m/s, and29.3%when the pulse frequency is2.5kHz. |
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