Numerical investigation of fill height and secondary currents in an inclined partially filled pipe flow

Partially filled pipes are used in industrial processes to transport liquid and particle laden flows. A good understanding of the three-dimensional flow in these pipes is critical to ensure material is transported without issue, for example without particulates settling out. In this work, air-water two-phase flows in a partially filled pipe geometry of an industrial slurry transport rig are investigated using unsteady Volume of Fluid (VOF) RANS model in OpenFOAM to investigate fill height and secondary currents. Both are important factors in partially filled pipes where the water depth and secondary current strength can influence solid particle transport and settling. The study confirms that the CFD approach can reliably predict the flow depth across a range of pipe inclination and the secondary currents are predicted in good qualitative agreement with those seen in other studies. The effect of pipe inclination on fill height and the effect of fill height on secondary currents are investigated for a range of mass flow rates. The results of fill height agree well with the experiments and are in line with the Manning equation for a hydraulically smooth pipe. Secondary current strength is seen to increase with fill height in agreement with other studies.