Numerical Simulation on Descaling Performance of Ultrasonic-Assisted Water Jet Under High Confining Pressure

Severe scale buildup threatens the safe operation of downhole tubing and subsea pipelines under high confining pressure. Conventional descaling methods are less effective in enclosed high-pressure environments, where elevated ambient pressure suppresses ultrasonic cavitation and the mechanism of ultrasonic-assisted jet descaling remains unclear. This study investigates the coupled effects of ultrasonic excitation and high-pressure water jets on descaling under high confining pressure. A numerical model incorporating a User-Defined Function (UDF)-based periodic pressure-pulsation boundary was developed to compare single-nozzle and three-nozzle configurations. The effects of nozzle configuration, jet pressure, nozzle diameter, ultrasonic frequency, and standoff distance on descaling performance were evaluated in terms of flow-field characteristics, scale-particle migration, and residual scale volume. The results show that ultrasonic excitation induces high-frequency pressure fluctuations while having little effect on the average jet velocity. The three-nozzle configuration provides broader flow coverage and better descaling performance. Increasing jet pressure and nozzle diameter enhances scale-particle motion. Among the investigated frequencies, 28 kHz produces the highest particle velocity for the three-nozzle configuration. A shorter standoff distance enhances jet impact intensity. This study provides insights into the effects of key operating parameters on ultrasonic-assisted jet descaling and establishes a numerical basis for parameter optimization under high-confining-pressure conditions.