Experimental characterization of smooth body flow separation topography and topology on a two-dimensional geometry of finite span

A smooth body, adverse pressure gradient (APG), turbulent boundary layer (TBL) separation is experimentally studied. The geometry features canonical TBI, development prior to encountering a smooth, two-dimensional convex ramp geometry of finite span onto which a streamwise APG that is fully adjustable is imposed. Both large- and small-scale separations are studied, and all data are archived on the NASA Turbulence Modeling Resource website. This paper describes the large-scale separation case with focus on the surface topography and topology of both separation and reattachment. Despite the spanwise uniform approach TBL and ramp geometry, the separation is highly three-dimensional but the reattachment is spanwise uniform. The surface flow topology is characterized by the 'owl-face pattern of the fourth kind' - found to be highly repeatable over multiple experiments. This ubiquitous topology has been reported for a variety of flows including inclined bodies of revolution. It is demonstrated that the APG and the secondary flow associated with the sidewall-ramp juncture is responsible for the formation of the surface separation patterns.

Automated summary

This experimental study investigates the turbulent boundary layer separation phenomenon on a smooth body under adverse pressure gradient conditions. The research reveals that the separation is highly three-dimensional, whereas the reattachment is spanwise uniform. The study also identifies a surface flow topology, known as the 'fourth kind owl-face pattern', which exhibits high repeatability across multiple experiments. It is demonstrated that the adverse pressure gradient and the secondary flow at the sidewall-ramp juncture are responsible for the formation of surface separation patterns.