On the experimental study of 3D turbulent shear layers*

Flow skewing in turbulent boundary layers is reported to cause a reduction in maximum Reynolds stresses and drag. However, definitive conclusions regarding 3D turbulent shear layers, or skewed shear layers—where merging shear layers have not only different speeds but also different directions—remain elusive. We experimentally investigated the mean flow and turbulence statistics of 3D turbulent shear layers in a wind tunnel to find out if boundary layers and shear layers display similar effects. We generated 3D shear layers by skewing the mean flow with turning vanes at the trailing edge of a splitter plate, and used pitot-static tubes and x-wires to probe the flow at different cross-, span- and downstream distances. The findings indicate that 3D shear layers, like their 2D counterparts, have self-similar-like mean velocity profiles, and spread approximately linearly with downstream distance. However, the 3D shear layers have larger thickness and reduced maximum Reynolds stresses in near-downstream region, while opposite trend is observed far-downstream when compared to the 2D case, suggesting reduced mixing as in 3D boundary layers.