Effects of Reynolds Number on Hydrodynamics in a 180-Degree Sharp Curved Channel Flow

Abstract

Reynolds number (Re) in the presence of curvature can alter the velocity field, the turbulence kinetic energy budget, eddy scales, and the anisotropic structure, initiate secondary circulations, and enhance three-dimensional anisotropy due to centrifugal and pressure-gradient imbalances. To understand these complex flow phenomena, a three-dimensional investigation is conducted in a 180-degree curved channel at various Reynolds numbers (Re). Instantaneous velocity was sampled within the curved reach using an Acoustic Doppler Velocimeter (ADV) at different probe locations along the curvature. In addition, Large Eddy Simulation (LES) has been performed to visualize the flow patterns and the growth of Dean vortices throughout the curvature. Results suggest that, as Re increases, the flow turbulence shifted from pancake-shaped to more cigar-shaped. The production and transport of turbulence kinetic energy, the pressure diffusion, and the turbulence dissipation rate decrease with increasing Re near the outer wall. Also, in the case of a locally produced turbulence kinetic energy, only 30-50% dissipates near the inner wall. Additionally, along the curvature, the primary vortices that generate the dominant frequencies and some small-scale vortices of varying sizes form near both side walls at the downstream. Moreover, the study of the velocity vector and bursting events using octant analysis revealed helical motion in the fluid at the highest Re. Also, the curvature-driven primary vortex near the inner wall is less influenced by turbulence.