SPH Simulation of High-Velocity Plunging Jets And Dynamic Loading in Plunge Pool Floors

High-velocity plunging jets are found in many dams as a way to discharge excess flood waters, with potential savings in expensive stilling basins. In recent years, the re-evaluation of the maximum probable floods, along with the acknowledged impact of climate change, has prompted reviews to the spillway’s capacity and operation scenarios. The inadequacy of many spillways’ capacity raises the possibility that dams might be overtopped during extreme floods, creating new hydrodynamic loading scenarios that may compromise the dam’s safety. Modelling plunging jets in laboratory presents a challenge due to the complex two-phase environment, which requires building models at near-prototype scales. Traditional computational investigations of plunging jets have been based on the well-settled Volume of Fluid (VOF) and Level Set (LS) methods, which implement a mesh on which to solve their partial differential equations. These methods, however, present some evident limitations, like the volume fraction function discontinuity across the interface. Unlike these approaches, the Smoothed Particle Hydrodynamics (SPH) method implements a meshless technique to solve the Navier-Stokes equations. It is particularly suited to model flows with complex free-surface patterns (e.g. fragmentations and air entrainment) and it has witnessed substantial developments in the last decade.

This paper presents the application of a 3D SPH model to study a circular jet impinging into a flat pool. The computational study uses the GPUSPH code to model the experimental facility and hydrodynamic conditions investigated by Manso et al. (2007). The study investigates the physics of the jet diffusion in the pool for shallow and deep pool conditions. At the pool bottom, the comparison between computed dynamic pressures and existing experimental data shows reasonable accuracy near the stagnation point, for shallow pool conditions. For deep pool conditions, the comparison shows larger differences, likely due to the absence of the air phase in the SPH model and difficulties to reproduce the jet diffusion in a strongly-aerated and macro-turbulent pool environment. To the authors’ best knowledge, there are no published studies regarding the prediction of dynamic pressures at the pool floor resulting from the impact of high velocity jets using SPH, at near-prototype conditions. The authors intend to build up on these preliminary results, by pursuing investigations on the flow features and the ability of the SPH method to reproduce two-phase flows.

Manso, P., Bollaert, E. and Schleiss, A. (2007) Impact pressures of turbulent high-velocity jets plunging in pools with flat bottom, Experiments in Fluids 42: 49-60.