Study on the optimal target distance of self-oscillation pulsed SC-CO2 jet based on resonant effect

Abstract

The SC-CO2 jet has broad application prospects in drilling engineering, but its promotion and application are limited by the high threshold pressure of coal breaking and system energy consumption. The high pulse pressure and resonance effects of the self-oscillation pulsed SC-CO2 jet can effectively reduce the threshold pressure of coal breaking and significantly improve the coal breaking efficiency. To fully utilize the resonance effect, based on the nozzle structure of the self-oscillation pulsed SC-CO2 jet, two nozzles with different pulse characteristics are used to study the comprehensive effect of pulse frequency and pressure amplitude at different target distances. The large eddy simulation was used to analyze the flow field structure of the jet, and the variation laws of the pulse frequency and pressure amplitude in the axial direction of the flow field were clarified. The effect of the target distance on the impact frequency and impact pressure of the jet was studied by the pulse characteristics test experiment, and the comprehensive effect of pulse characteristics on coal breaking was studied by coal breaking experiments. The results show that the pulse frequency and pulse pressure amplitude of the self-oscillation pulsed SC-CO2 jet do not remain constant in the axial direction of the jet, and they gradually decrease with the increasing target distance. Considering only the pulse frequency cannot maximize the resonance effect, and it is necessary to comprehensively consider the influence of pulse frequency and pressure amplitude on the resonance effect. Using displacement response amplitude to characterize the resonance effect can reflect the comprehensive influence of frequency and amplitude on resonance. When the target distance is small, from 0 mm to 13 mm, the main influencing factor of the displacement response amplitude is the pulse pressure amplitude; when the target distance is large, from 13 mm to 26 mm, the main influencing factor changes to the pulse frequency. In addition, reducing the pulse frequency and increasing the pressure amplitude can effectively improve the displacement response amplitude. Under the conditions of nozzle structure with different pulse characteristics, the transition positions of the main influencing factors of displacement response amplitude are different, and the optimal target distance is also not the same. Both nozzles achieve the best coal breaking effect at the maximum displacement response amplitude, which indicates that the displacement response amplitude can be used as the criterion to judge the optimal target distance. In this paper, the dimensionless optimal target distances of nozzle a and nozzle b are 7 and 9 respectively.