Numerical Modeling for Periodic Oscillation of Free Overfall in a Vertical Drop Pool

Abstract

This study numerically investigates the effect of various plunge pool lengths on the flow conditions with a fixed subcritical approach flow because the flow regimes of free overfall in a vertical drop pool can be mainly classified into skimming, nappe, and periodic oscillatory flows depending upon different discharges and pool dimensions. The simulated water surface and oscillatory period compare well with the experimental data. After the correctness of the numerical model is validated, the velocity and vorticity contours are examined to explore the surface jet of the skimming flow, the impinging jet of the nappe flow, and the dropping flow switching between these two jets. The effect of an air pocket underneath the dropping jet on the oscillatory behavior is addressed, as well as the kinetic and potential energy evolutions are discussed in view of control volume analysis during the periodic oscillatory process. Finally, the authors calculate the hydraulic head loss to evaluate the energy dissipation efficiency with various drop pool lengths for different flow regimes.