The Effects of Pressure Gradients and Surface Roughness on Turbulent Boundary Layers

The effects of pressure gradients applied to a flat surface with heterogeneous roughness for turbulent boundary layers is not well understood. The current study experimentally investigates this fundamental interaction by characterizing the development of a turbulent boundary layer over a flat plate with strips with different roughnesses, each 0.10 m wide by 3.7 m long, subjected to both favorable and adverse pressure gradients. The study is performed in the Portland State University wind tunnel with a test section of 5 m in length, 1.2 m in width, and 0.8 m in height. The adverse and favorable pressure gradients are applied to the plate by adjusting the angles of the ceiling panels of the wind tunnel such that flow separation does not occur at any point along the plate, which would occur if the plate itself were tilted. Boundary layer development for each case is characterized based on particle image velocimetry data.