Andrea Del Gaudio

The study investigates the evolution of a dam break wave of a mixture of clay and water in turbulent flow conditions and its interaction with a vertical rigid wall. The phenomenon reproduction, important for planning risk mitigation strategies and designing protective structures, is performed by means of three-dimensional large eddy simulations. The dynamical Smagorinsky model is employed and the volume-of-fluid technique is used to calculate the free surface evolution with time. A power-law model is considered to represent the mixture rheology. With reference to a small-scale setup, the paper analyzes the influence of the clay concentration and of initial fluid depth upstream of the lock gate on the temporal evolution of the front, the bed shear stresses, and the force acting on the vertical endwall. Moreover, the presence of three-dimensional effects and the turbulence role are also investigated. The occurrence of scale effects for the non-Newtonian dam break wave is finally examined by performing an additional test with a larger-scale setup. Results indicate that lobelike structures develop near the front of the current and near-bed streaks of low and high velocity are present behind the front. The variation of the wave front position with time is described by a power-law function, independently of both clay concentration and initial fluid depth. Over the body of the current, the nondimensional bed shear stress values in the simulations performed with non-Newtonian fluids are about two times larger than the ones in the clear water case. Moreover, the peak value of the nondimensional impact force, slightly lower than the one in clear water, decreases when clay concentration is increased. Comparing large- and small-scale tests, higher nondimensional propagation speeds and bed shear stress values in the front region are observed in the former one. Conversely, the nondimensional peak force is not affected by scale effects, suggesting that small-scale tests can be used to provide reliable predictions of this critical variable for engineering design.

Summary: Dam‐Break waves arise from the sudden release of the water stored behind a wall, and they cause destruction and losses on nearby areas. Characterisation of the impact force on obstacles is very important for risk assessment. In this work, we performed a series of lock‐release experiments to evaluate the wave‐induced impact force on a vertical end wall situated some distance from the lock. Laboratory data were used to evaluate the performance of several types of numerical models to predict the wave‐induced force on the vertical end wall. The selected models were as follows: the hydrostatic 1D De Saint‐Venant model, the multi‐layer hydrostatic model and the Navier–Stokes two‐phase flow. For the latter two models, both 2D (in the ‐ plane) and 3D simulations were performed. The results show that, independently of the hydrostatic assumption, the 2‐D simulations generate nonphysical oscillations which are not present in the measured temporal histories of the pressure and force values. By contrast, the predictions of both 3D numerical models better reproduce the temporal variation of the pressure forces on the end wall. The present study also shows that from a practical point of view, the 1D De Saint‐Venant model predicts with sufficient accuracy the impact time and the magnitude of the peak value of the impact force. Therefore, if the use of a fully 3D models is not a feasible option, in terms of a trade‐off between computation cost and accuracy, the use of a simple hydrostatic 1D De Saint‐Venant model is preferable to a 2D model.

Tsunamis, impulse waves, and dam break waves have a high impact on nearby areas. Scaled experiments allow us to deeply understand the hydrodynamic features of these unsteady flows and, equally, to validate numerical models. The study shows the experimental set-up and the preliminary results of the tests performed at the Hydraulic Engineering Laboratory of the University of Naples “Federico II”. We set up a 3 m long Perspex tank in order to generate dam break waves by a pneumatic gate removal. Two high-speed CCD (charge-coupled device) cameras were used to characterize the wavefront celerity and the free surface profile. Five pressure transducers were installed on a vertical wall, located at the end of the channel, in order to sample the force extent of the surge. The results of the numerical simulations realized through the depth-integrated model were compared with experimental data.