Large eddy simulation of power-law fluid dam break wave impacting against a vertical wall

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.