Roughness Effects on Super Structures in Turbulent Boundary Layer Flows

This study investigates the influence of wall roughness on large-scale structures within turbulent boundary layers, using wall-parallel stereoscopic Particle Image Velocimetry (PIV) at a Reynolds number of 1.3 × 106m−1. The data was collected at a distance of = 2.8 from the wall under adverse = 0.98, small = −0.04, and favorable = −0.60 pressure conditions. It was observed that coherent structures larger than the field of view (FOV) modify their length scales, streamwise orientation and spanwise distribution in response to changes in surface roughness and pressure gradients. The study also examines implications wall similarity hypothesis by comparing the development of these large-scale structures over smooth and rough wall flows under small pressure gradient and identical test conditions. Notably, the results reveal that existing models may not accurately capture the observed dynamics, as evidenced by discrepancies with previous studies, thereby enhancing our understanding of turbulent flow dynamics in non-equilibrium conditions.