Abstract
The self-oscillating pulsed supercritical (SC)-CO2 jet technology has higher pulse pressure and the resonant rock-breaking effect, which can improve the drilling efficiency of the development of unconventional gas sources. The jet impact frequency is the key to resonance in coal rock mass; however, the relationship between frequency variation and flow field remain unknown. This study investigates the vortex change law and the effect on frequency of self-oscillating pulsed SC-CO2 jets. Large eddy simulations are used to analyze the variation characteristics of vortex structure and frequency at different locations of the jet. The results show that the variation of the vortex size in the oscillating cavity leads to the change of the jet velocity. Large-scale vortex is generated at the downstream nozzle exit and is accompanied by a high-speed zone of the jet, vortex development produces energy dissipation, which decreases the velocity in the high-speed zone. The jet frequency in the oscillating cavity is the same as the vortex ring size variation law; the vortex passing frequency in the free flow field is the same as the jet frequency, and the vortex ring energy dissipation causes the jet velocity to decrease, resulting in a lower frequency.
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