Experimental and Numerical Investigation of Multi-Regime Oil Leakage from Underwater Pipelines

In this study, experimental investigations combined with numerical simulations were conducted to elucidate the multi-regime evolution and migration characteristics of underwater oil leakage. The effects of oil density, viscosity, leakage mass flow rate, orifice diameter, and water depth on oil-phase morphology, plume evolution, and surface arrival behavior were systematically analyzed.

The experiments revealed three typical leakage regimes, including discrete-droplet flow, transitional-breakup, and atomized-plume, with increasing leakage intensity. A dimensionless regime map based on Reynolds (<i>Re</i>) and Ohnesorge (<i>Oh</i>) numbers was established to characterize the transition among different leakage states. According to the identified flow regimes, two numerical approaches were employed: the Volume of Fluid (VOF) method was used for droplet/jet-dominated leakage with resolvable oil-water interfaces, while the coupled VOF-Discrete Phase Model (VOF-DPM) approach was adopted for atomized leakage involving fine oil droplets.