An experimental investigation of the turbulent boundary layer over 2D roughness with localized blowing*

The effects of localized blowing (injection) on the turbulent boundary layer over large-scale 2D k-type roughness was experimentally investigated using planar and volumetric particle image velocimetry. The roughness was composed of identical transverse square bars at a pitch to height ratio p∕h = 11. The experiments were conducted at a Reynolds number of 100,000, based on the boundary layer thickness and the free-stream velocity, and the bars occupied ∼14% of the boundary layer thickness. In addition to a baseline no-injection case, localized blowing through five small spanwise jets was considered for two streamwise locations and at two injection rates. The volumetric flow rate through the jets was below 0.12% of the overall volumetric flow rate, resulting in a small perturbation to the flow field. The results highlight the effects of localized blowing on the time-averaged flow, boundary layer characteristics, and Reynolds stresses. The effects of localized blowing on the boundary layer turbulence structure are also investigated thorough two-point correlations and proper orthogonal decomposition.