Transformation and intensification of tornado-like flow in a narrow channel during elongation of an oval dimple with constant area

Reynolds averaged Navier–Stokes equations closed using the Menter shear-stress-transfer model have been numerically solved on multiblock intersecting structured grids of various scales. The obtained solution has been used to analyze the separated flow past an elongated oval dimple oriented at 45$^\circ$ on the wall of a narrow plane-parallel channel and to study transformation of the flow with increasing dimple aspect ratio at constant depth and spot area. It is established that, at a dimple width below one-third of the equivalent dimple diameter, intensification of the generated helical vortices observed when the transverse flow velocity exceeds 80% of the average mass flow velocity is accompanied by decrease in the level of hydraulic losses below that in an otherwise identical channel with an equivalent spherical dimple.