Vortex dynamics and air entrainment in dam break wave impacting on vertical walls: A multiphase lattice Boltzmann study

Abstract

Air entrainment often plays a crucial role in determining impact loads exerted by free-surface wave flows interacting with structures, yet its modelling is often oversimplified in numerical approaches. In this study a two-phase numerical model, based on the Lattice Boltzmann Method coupled to a conservative Allen--Cahn interface-capturing equation is employed to perform direct numerical simulations of dam-break waves propagating over a dry bed and impacting on vertical walls. Access to high-resolution simulations enables a detailed assessment of how accurately resolving both air--water and solid--water interfaces affects local and overall dynamics, as well as quantities of extreme engineering interest. Indeed, the magnitudes and locations of the pressure peaks are strongly affected by wave front deflection and local aeration induced by a small corner vortex. Additionally, comparisons between no-slip and free-slip implementations suggest that the large air cavity formation, commonly observed as trapped inside the reflected jet falling back onto the incoming flow, may be the result of modeling assumptions rather than intrinsic flow physics, again highlighting the key role of near-wall shear in jet breakup dynamics.