Pigging Oil Flow in a Pipeline: VOF Model

Description

This project uses ANSYS Fluent to simulate pigging oil flow inside a pipeline, a core operational process in gas and petrochemical pipeline engineering. A "pig" (Pipeline Inspection Gauge) is a device used inside pipelines for inspection, cleaning, and separating different fluid batches. Because a pig acts as an obstruction to flow, it introduces a pressure drop across its body — a key flow assurance concern this simulation investigates. The model examines fluid behavior around a stationary pig and the resulting pressure drop on either side, under two inlet oil velocities (0.9 m/s and 1.9 m/s).

Methodology

The 2D geometry, consisting of a pipeline with a simple pig inside it, is built in DesignModeler and meshed in ANSYS Meshing using an unstructured grid of 5,789 elements. The simulation uses a pressure-based, transient solver, run for 90 seconds with a 0.03 second time step, with gravity neglected. Turbulence is modeled using the standard k-epsilon model with standard near-wall treatment. The VOF multiphase model defines two fluid phases — gas-oil and petro — using implicit formulation with sharp interface modeling to track the boundary between them.

Boundary conditions specify a velocity inlet (0.9 or 1.9 m/s) with a petro volume fraction of 1 and gas-oil volume fraction of 0, a pressure outlet at 0 Pa gauge, and stationary walls for both the pipeline and pig surfaces. The solution uses the SIMPLE scheme for pressure-velocity coupling, PRESTO for pressure discretization, second-order upwind for momentum, a compressive scheme for volume fraction, and first-order upwind for turbulence quantities, with standard initialization at zero gauge pressure and zero petro volume fraction.

Conclusion

Results include 2D contours of pressure, velocity, and phase volume fraction for both inlet velocity cases, evaluated at the final second of simulation. These results characterize the pressure drop and flow disruption caused by the pig, directly informing pipeline pigging operations and pressure loss management in oil and gas transport systems.