Volumetric Time-Resolved Flow Measurements of Rough-Wall Turbulent Boundary Layers with Flow Injection

Roughness increases drag in countless engineering systems; as such, understanding the turbulent flow over rough surfaces is an essential engineering task. One possible way to control turbulent flow over roughness is through blowing, which is the focus of my senior project. Volumetric particle image velocimetry (PIV) was used to experimentally study the effects of localized blowing on the turbulent boundary layer over two-dimensional k-type roughness. The experiments were performed at a Reynolds number of 100,000, based on the boundary layer thickness and the freestream velocity. Flow measurements were performed at a channel flow rate of 1 m/s for 5 cases including a baseline no-injection case. The additional four cases included localized blowing through five small spanwise jets considered at two rates and two injection locations. Flow organization was found to be maintained across all five cases due to the relatively small volumetric flow rate of the jets: below 0.12% of the overall flow rate. Localized blowing was found to alter the time-averaged streamwise velocity, boundary layer characteristics, Reynolds shear stress, and turbulent kinetic energy. Volumetric measurements were able to capture variations of up to 18% in reattachment length in the spanwise and other spanwise variation in the flow quantities listed above. The volumetric measurements also enabled the visualization of flow coherent structures including the counter-rotating vortex pair associated with each jet.