Turbulent flow over transverse ribs in open channel with converging side walls

This paper reports an experimental study of favorable pressure gradient turbulent flow over transverse square ribs in an open channel. The first half of the channel test section has straight parallel side walls, and each of the side walls of the second half of the test section converges linearly to produce the favorable pressure gradient. Two different values of half-angle (α = 1° and 2°) of the converging side walls were used to vary the pressure gradient. For each value of α, transverse square ribs were glued onto the bottom wall both upstream of and within the converging sections. The pitch-to-height ratio of the ribs was varied to produce d-type, intermediate and k-type rib roughness. A particle image velocimetry was used to conduct detailed measurements over the ribs at several planes upstream of and within the converging sections. From these measurements, mean velocities and turbulent quantities were extracted at selected streamwise locations. The distributions of the mean velocities, turbulent intensities, and the mean and turbulent momentum fluxes at the interface between the rib cavities and the overlying boundary layer were used to provide insight into the interaction between the shear layers. The profiles of mean velocity, turbulent intensities, Reynolds shear stress and triple products were obtained to document the characteristics of favorable pressure gradient turbulent flow over square ribs in an open channel.