Occurrence of Naturally Shaped Lenticular Bed Deposit and Its Influence on the Frictional Pressure Drop during Pipeline Transportation of Low Concentration Slurries

摘要

Solid particles can be transported along a pipeline in the form of trains of individually shaped lenticular deposits (LDs) when the concentration of solids is less than 1 vol% and the transport velocity is below the critical value required for full suspension. Such special bed transport, observed as rippled sand dune patterns, may occur in petroleum production lines transporting oil and gas produced from unconsolidated sand reservoirs under turbulent flow conditions, and during sediment transport by rivers and winds. The primary objective of this study was to investigate how the occurrence of lenticular bed deposits affects near-wall turbulent activities at the sand/fluid ("wave-like") interface and frictional pressure drop during pipeline transportation of solids. Particle image velocimetry (PIV) measurements were used to quantify the velocity field, the turbulence kinetic energy (TKE), and the coherent structures associated with surface morphology change and LD formation near the bed deposits/fluid interface. A 7-8% reduction in frictional pressure drop was consistently observed during the transition from continuous sand bed to LDs. Results also indicate that the formation of naturally shaped LDs reduces the intensity and frequency of near-wall turbulent coherent structures (burst-sweep events). Moreover, TKE associated with flow over the LDs was found to be lower than that of continuous bed and water (only) flow.