The wake of a single 2D roughness element immersed in a turbulent boundary layer

Measurements are presented of a fully-developed zero-pressure-gradient turbulent boundary layer interacting with a single 2D roughness element. Mean velocity profiles were measured using 2D PIV over a smooth surface and a single roughness element. The roughness element was a square bar with cross-sectional dimensions of 10 mm x 10 mm and a length of 0.9 m. The experiments were conducted in the turbulence research water tunnel at Cambridge University, and at Reynolds numbers (based on the momentum thickness) ranging from 3016 to 4670. Velocity defect profiles were analyzed using three different outer velocity scales: friction velocity (u T ), freestream velocity (U ∞)1 (Fig. 1) and, mixed outer scale $\left( {\frac{{U_\infty \delta ^* }}{\delta }} \right)^2$ A discussion is presented of the wall-normal extent of the wake and of how it evolves with streamwise distance and different Reynolds numbers