Near-wall turbulence of semidilute polymer solution flows subjected to varying favourable pressure gradient

High-resolution particle image velocimetry was employed to investigate the near-wall boundary layer (BL) in viscoelastic polymeric flows subjected to pressure gradient (PG) effects in a mesoscale water channel. The flow was driven over a converging surface with varying favourable PG (V-FPG), a flat surface with constant FPG (C-FPG), and a diverging surface with varying adverse PG. This study examines the interplay between viscoelasticity and FPG in shaping BL dynamics. Velocity statistics measured on the channel mid-plane are reported for Newtonian water and non-Newtonian polyacrylamide solutions at concentrations of 200~p.p.m. and 400~p.p.m., with and without PG effects. In fully developed C-FPG polymeric flows, mean streamwise velocity fluctuations increased markedly with concentration, with peak dimensional values enhanced by ≈58% and ≈87% at the highest flow rates compared to water. Accelerating polymer solution flows exhibited elevated edge-to-mean velocity ratios and relaminarised regions in the converging section due to strong FPGs. Inner-normalised mean velocity profiles deviated from the classical log law depending on the local PG and skin friction. The combination of V-FPG and polymer viscoelasticity strongly suppressed Reynolds shear stresses, with peak dimensional values reduced by ≈80% and ≈89% in accelerating 200~p.p.m. and 400~p.p.m. flows relative to water. These findings provide new insights into the coupled effects of PGs and viscoelasticity on wall-bounded turbulence, offering guidance for improved numerical modelling and engineering design in complex flow systems.