Mixing process in opposing flow junction with different angles and junction radii

Opposing flow junctions are considered as important elements in thermal and hydraulic equipment. This study numerically investigates the effects of angles and junction radii on coherent flow structures at opposing flow junctions with subcritical conditions. Hence, the three-dimensional unsteady Reynolds-averaged Navier–Stokes equations are solved with the k–ε turbulence model on a non-staggered grid using the indirect addressing treatment. After the verification of the numerical model, several numerical simulations are conducted for angles 35°, 40°, 45°, 50°, 60°, 70°, 80°, and 90° with different upstream Froude numbers and junction radii. The streamwise-oriented vortical cells only elongate into the branch channel of the opposing flow junction with angle 90°. By decreasing the angle between the main channel and confluent tributary, these cells decay in the main channel width, and one of the separation zones is gradually eliminated, as that does not form in the opposing flow junctions with angle 40°. The enhancement of junction radii decreases the dimensions of the separation and stagnation zones. Numerical simulation results of a curved-edge opposing flow junction with angle 80° indicate that any of the streamwise-oriented vortical cells in the main channel and separations zones in the branch channel are not formed. In such a condition, three vortical cells formed along the branch without decay, two cells are located near the side wall, and another cell is near the free surface.