Study on the evolution law of the vortical structure inside of oscillation chamber of self-excited oscillation pulsed supercritical carbon dioxide jet (SEOP SC-CO2 jet) and its influence on pulsed characteristics

The self-excited oscillation pulsed supercritical carbon dioxide jet (SEOP SC-CO2 jet), known as a novel and efficient drilling method, holds extensive potential for various applications. Maximizing the benefits of pulsed jet requires focused consideration of the pulsed frequency and pressure that engage with the coal. Consequently, the focus of this study was on the influence mechanisms of pulsed frequency and pulsed pressure. This study examined the vortical structure inside of oscillation chamber, its internal frequency and pressure, along with the jet's pulsed frequency and pressure. It elucidated that how the evolution law of the vortical structure influenced the pulsed frequency and pulsed pressure, leading to the identification of the influence mechanism. The study also analyzed how the chamber diameter proportions regulated this influence mechanism. Finally, the experimental tests on the pulsed frequency and pulsed pressure of the jet were carried out. The results indicate that by modifying the frequency and pressure inside of oscillation chamber, the vortical structure's feedback movement, along with the dynamics of expansion and compression inside of oscillation chamber, regulate both the pulsed frequency and pressure of the SEOP SC-CO2 jet. The downstream nozzle minimally affects the flow pattern of vortical structure and the dynamics of expansion and compression, ensuring the jet's pulsed frequency and pressure align with those inside of oscillation chamber. By altering the vortical structure's feedback movement and the dynamics of expansion and compression, the chamber diameter proportions regulate both pulsed frequency and pressure. As the chamber diameter proportions expand, the dimension of the vortical structure, the frequency inside of oscillation chamber, and the pulsed frequency follow a pattern of initial increase and subsequent decrease, in contrast to the pressure inside of oscillation chamber and the pulsed pressure, which start with a decline, then an increase, and ultimately a fall. Furthermore, the chamber diameter proportions will affect the specific location where vortex pairs occur in the freestream flow, leading these pairs to a halving of the pulsed frequency and a temporary enhancement in pulsed pressure.