A-type hydraulic jumps over a negative step: Numerical investigation based on composite modeling and validation

Abstract

Numerical modeling of the rapid transition at a hydraulic jump is challenging considering the complex coupling between air transportation and turbulence evolution at various length scales. In this paper, the turbulent air-water flow properties in A-type hydraulic jumps over a negative step were investigated and compared to those in classic hydraulic jump numerically. The model solves the Reynolds-averaged Navier-Stokes (RANS) equations for mean flow motion, the modified k-ϵ model for turbulence closure, and an advanced transient model for void fraction distribution. The numerical model was validated by systematically comparing the simulated free-surface profile, time-averaged velocity and void fraction distributions against experimental results developed in parallel to the numerical modeling. The validated model reproduced successfully the basic air-water flow properties, including the formation of a bottom roller in the step cavity below the A-type jumps. The simulation revealed further turbulence characteristics of the aerated flow and their evolution over the abrupt drop. The stepped bottom introduced secondary vorticity in the lower shear layer that enhanced energy dissipation and reduced the bottom boundary shear force, thus providing bed surface protection. It was also able to help with stabilization of the hydraulic jump position by weakening the jump toe oscillation.