Wall Slip Mechanism During Flow Startup of a Pipe Filled with Complex Fluid Exhibiting Yielding Behavior

Wall slip during flow startup operation involving gelled fluids like polymers, emulsions, etc. is mostly overlooked during numerical analysis. Hence, one may potentially misinterpret the fluid mechanics associated with the gel’s degradation and its subsequent clearance from the pipeline. In our study, we decipher numerically that the wall-slip mechanism modifies the net rheology governing the gel degradation at the bulk of the pipeline. The wall slip causes faster initial pressure wave propagation across weakly compressible-based fully homogeneous gelled pipelines during the flow startup operation. At a later time, the effect of wall-slip alleviates, and the bulk deformation dominates the proceedings. The intuition of low gel deformation for the case of wall slip-induced flow (compared to the scenario of no-slip) during initial compressive pressure propagation is not true in our present study. This is also verified through local variations in flow velocity and strain near the wall. This outcome is consistent across various types of complex fluids like elasto-viscoplastic and shear-thinning fluids. The mathematical model used in this study successfully replicates features like thixotropy, strain-dependent yielding behavior, and slip-stick mechanism at the wall-fluid interface.