Wall Shear Stress Measurements In Water By Molecular Tagging Velocimetry At High Spatio-Temporal Resolution

The wall shear stress is one of the most important (if not the most important) quantities to resolve for many applied fields, including naval hydrodynamics and aerodynamics. In high-Reynolds number flows, it cannot be simulated directly and one is forced to use models that rely on wall shear stress data to be developed and validated. However, measuring wall shear stress at high Reynolds number is very challenging, especially in water. Here, we deploy molecular tagging velocimetry by photobleaching of rhodamine 6G. Combined with Talbot-effect structured illumination, we reach both high temporal and spatial resolutions directly at the wall. The flow is a Reτ ≈ 800 and 1,200 turbulent channel flow, which enables to calibrate the accuracy and precision of the technique.