Analysis of the Scale Ratio in Nappe Flow Case by Means of CFD Numerical Simulation

Rectangular jet or nappe flow constitutes one of the energy dissipation methods in arch dams. The high turbulence and aeration phenomena that appear in fall jets and dissipation basins make difficult to carry out their characterization only based in classical methodologies: reduced models and empirical formulae. The Hydraulics Laboratory of the Universidad Politecnica de Cartagena (Spain) has an infrastructure designed specifically for the study of turbulent jets and energy dissipation in plunge pools. The device allows us to study air-water two-phase phenomena (aeration, spray, spread and impact). The mobile mechanism lets us to vary the discharge heights between 1.70 and 4.00 m and flows between 10 and 150 l/s. To improve the knowledge of the phenomenon of turbulent jets, we are measuring aeration rates by means of fiber optical equipment, velocities in different sections of the stilling basin with Doppler instrumentations and pressures on the bottom of the plunge pool with piezoresistive transducers. Computational Fluid Dynamics programs (CFD) are based on numerical solution of the Reynolds Averaged Navier-Stokes (RANS) equations, together with turbulence models of different degrees of complexity. The programs simulates the interaction between different fluids, such as the air-water two-phase flows, and constitute a new and powerful tool that could let contrast and complement the lab measurement. There are many studies modeling spillways with CFD methodology using different eddy viscosity turbulence models with accurate results. However, the study of overflow nappe impingement jets has not been sufficiently studied. Scale effects are important effects that need to be taking account. In this study, numerical simulations has been carry out using different scales ratio of the lab device according to Froude similarity (1:1; 1:10; 1:20 and 1:40). This paper compares the Parametric Methodology proposed by Castillo (2006, 2007) for the evaluation of hydrodynamic action in plunge pools, revised by Castillo and Carrillo (2011, 2012), with more and new laboratory measurements and the simulation results obtained with CFD program.