The effects of concave curvature on turbulent boundary layer structure

Concave curvature has a relatively large, unpredictable effect on turbulent boundary layers. Past studies have emphasized quantitative single point measurements. Some of these studies have suggested that a large scale, stationary array of counter-rotating vortices exists within the turbulent boundary layer on a concave wall. The objective of the present study was to obtain a qualitative model of the flow field in order to increase our understanding of the underlying physics and thereby guide future work. A large, free surface water channel was constructed in order to perform a predominantly visual study of the flow. Dyes and hydrogen bubbles were used to mark the flow. Streamwise components of mean velocity and turbulence intensity were measured using a computer controlled hot film anemometer. Velocity measurements upstream of the start of curvature showed the boundary layer to be acceptably spanwise uniform with a momentum thickness Reynolds number of 1300.