Author(s): Joongcheol Paik; Hongjoon Shin
Linked Author(s): Joongcheol Paik
Keywords: Open channel flows; Turbulence; Coherent structures; Drop structure; Numerical simulation
Abstract: Turbulent flow behavior is highly sensitive to abrupt changes in solid interfaces such as topography and hydraulic structures. When flow passes through a stepped structure, vortices shed from sharp edges of the structures. The shear layer induced by flow separation and subsequent reattachment lead to flow recirculation downstream of the structure. The dynamics of the coherent structures and their behavior depend on the Reynolds number of flow. A previous study of Kim and Paik (2022), which used the Reynolds-averaged Navier Stokes (RANS) equations along with k-ω shear stress transport (SST) model and the RNG k-ε model, showed that both RANS models could reasonably reproduce the time-averaged velocity distributions from the experiments of Nakagawa and Nezu (1987). However, the study found that both models significantly underestimated the Reynolds stresses observed experimentally downstream of the sharp edge of the drop structure. Kim and Paik also applied a hybrid LES/RANS approach to address the limitation of RANS simulations, using pre-calculated steady inflow conditions. However, their findings indicated that applying unsteady turbulent inflow conditions is crucial for obtaining reliable numerical results. Otherwise, the hybrid LES/RANS approach may yield inaccurate solutions, even for time-averaged velocity components, compared to traditional RANS simulations.
Year: 2025