Modelling two- and three-dimensional separation from curved surfaces with anisotropy-resolving turbulence closures

The ability of non-linear eddy-viscosity and second-moment models to predict separation from two- and three-dimensional curved surfaces is examined on the basis of computations for two flows that are geometrically akin: one separating from periodically-spaced, two-dimensional `hills' in a plane channel, and the other from a three-dimensional hill in a duct. One major objective is to examine whether the predictive performance in 3-d (three-dimensional) conditions relates to that in 2-d (two-dimensional) flow. In the former, the separation pattern is far more complicated, being characterised by multiple vortical structures associated with `open' separation. The predicted separation behaviour in the 2-d flow differs significantly from model to model, with only one non-linear model among those examined performing well, this variant formulated to adhere to the two-component wall limit. In 3-d separation, none of the models gives a credible representation of the complex multi-vortical separation pattern.