Three-dimensional CFD analysis of liquid slug acceleration and impact in a voided pipeline with end orifice

Abstract

This research describes the dynamic behavior of an isolated slug driven by pressurized air in a voided line with an end orifice. A three-dimensional (3D) computational-fluid-dynamics (CFD) model is used to simulate the rapid propulsion and impact at the orifice for given slug length and driving air pressure, and is validated against experimental data. New mechanisms are observed: (i) the driving air pressure at the slug tail decreases with the slug motion; (ii) when the slug arrives at the orifice, the air fraction is almost one hundred percent in the most upstream part of the pipe, then it attenuates rapidly until an invariant eighty percent is achieved with a constant mass shedding rate; (iii) the velocity distribution in the radial direction of the cross-section at the midpoint of the slug length evolves from uniform to trapezoidal and then to logarithmic during slug movement; (iv) the initial vertical slug front changes its shape due to air intrusion at the top of the slug front; (v) the slug’s acceleration decreases first and then increases under the combined effects of its decreasing mass, nonlinear attenuation of the driving pressure, and increasing skin friction; (vi) the slug length has a constant rate of decrease.