Experimental investigation of turbulence in non-Newtonian fluids using ultrasound velocity profiling

Transportation of non-Newtonian fluids (NNFs) through pipelines is a cornerstone of modern infrastructure. While the laminar and transitional flows have been extensively studied, the turbulent behavior of NNFs remains poorly understood. This study investigates large-scale pipe-loop experiments on clay–water slurries, spanning Reynolds numbers ≈ 1 . 1 × 1 0 4 – 1 . 75 × 1 0 5 in a 100-mm diameter facility. Using non-invasive ultrasound velocity profiling (UVP) together with wall shear stress measurements, we characterize flows ranging from weakly to highly non-Newtonian conditions with concentrations up to 19%(w/w). The experiments show that the transition to the log-law region is delayed and the log-law intercept shifts upward with increasing concentration, reflecting the redistribution of stresses as shear-thinning and yield effects become more pronounced. To further interpret these findings, the experimental observations were compared with established modeling approaches. Semi-empirical correlations exhibited intermediate performance (mean absolute error, MAE, up to 0.55 Pa for wall shear stress and 0.15 m/s for velocity), while the Launder–Spalding wall function performed worst due to its assumption of constant viscosity (MAE ≈ 1.48 Pa and 0.08 m/s). In contrast, the rheology-based wall function achieved the most reliable predictions, with minimal deviations from experiments (MAE ≈ 0.20 Pa for wall shear stress and 0.06 m/s for velocity). Overall, this work provides a comprehensive experimental and modeling assessment of turbulent non-Newtonian pipe flow at an industrial scale, yielding new insights into flow physics and establishing a valuable reference for future experimental and computational studies. • Large-scale UVP experiments quantify turbulent flow of non-Newtonian clay–water slurries. • Increasing shear-thinning delays transition and shifts the logarithmic-law region upward. • Rheology-based wall functions yield the most consistent stress and velocity predictions. • Infinite-viscosity models and high-shear-rate rheometry improve accuracy at extreme flows.