Research papersInvestigation of water-water interface in dam break flow with a wet bed

•A modified two-liquid VOF method is proposed to capture both the free surface and water-water interface.•The numerical model provides good results at the initial stage and long channel propagation of dam break flow.•The initial stage of dam break flow is affected by gate thickness, gate removal velocity and ambient water depth.•Propagation of dam break wave front is faster than the propagation of water-water interface.

The evolution of water-water interface between reservoir and ambient water in dam break flow with a wet bed is numerically investigated based on a two-liquid Volume of Fluid (VOF) method. The VOF method is employed to capture both the free surface and water-water interface under Eulerian grids. The modification to VOF method prevents the intersection problem from happening on the water-water interface. The initial stage and long channel propagation of dam break flow are investigated numerically according to the experiments of Jánosi et al. (2004) and Ozmen-Cagatay and Kocaman (2010). The comparison of free surface and water-water interface evolution have good agreement with the published experimental and numerical results. The evolution of water-water interface at the initial stage of dam break flow and the analysis of gate thickness, gate removal velocity and ambient water depth effects are further examined. Besides, propagations of dam break flow in a long channel are investigated, a time difference between the propagation of water-water interface and dam break wave front is found.