Implementation of a 3D-PTV System for Interrogating Turbulent Boundary Layer Development Post Reattachment of a Backward-Facing Step Flow

Abstract

In this study, the turbulence behavior post reattachment of a backward-facing step flow, typically within the initial redeveloping boundary layer was present. An experimental technique, 3D particle tracking velocimetry (3D-PTV), was applied to collect three-dimensional velocity vector fields. Experiments were taken under inlet velocity uin = 17.89 cm/s, corresponding to a step-height Reynolds number Reh = 5100. In this PTV system, four 2560 x 1600 px2 CMOS cameras were used to capture images of a 47.6mm x 28.7 mm x 9mm volume of interest, which was located at ~7.5h downstream from the edge of the step in a water tunnel. The volume seeded with high-dense silver coated hollow glass particles was illuminated by a dual-pulsed Nd:YAG laser at 15Hz, Δt=700 µs. Insight 4G V3V software (TSI, Inc.) was applied to collect paired images, and run particle identification, particle matching, and particle tracking. Utilizing the acquired data, a series of vortices’ motions in the boundary layer were clearly shown with flow visualization. Meanwhile, quantitative data such as time-averaged velocity profile, Reynold stresses, and turbulent energy spectrum were acquired, and further compared with previous publications. The data of collected velocity field in the present study will provide a basis for which to examine the use of this system for future investigations of Subgrid-Scale Modeling (SGS) testing with experimental data.