Lock exchange gravity currents on upsloping beds

This work deals with gravity currents moving on upsloping beds investigated by both experimental and numerical simulations. Laboratory experiments were realized by the lock exchange release technique in a Perspex tank of rectangular cross section, divided into two reservoirs by a vertical removable gate, one filled with colored salty water and the other one filled with clear fresh water with a lower density. When the gate is removed, the dense fluid collapses developing a gravity current under the surrounding fluid. Different values of the bed’s slope were tested. Each experiment was recorded by a CCD camera and an image analysis technique, based on the threshold method, was applied to measure the space-time evolution of the current’s profile and the time history of the front’s position. Numerical simulations were carried out using a two-layer shallow water model, which accounts for both the free surface and the mixing between the two fluids. Two different relations are used to model the entrainment: the formula suggested by Adduce et al. (2012) and the formula of Cenedese & Adduce (2010). A comparison between numerical and experimental results was performed. Numerical simulations performed with Adduce et al. (2012) formula show a better agreement with the experimental results, if compared with the simulations using Cenedese and Adduce (2010) relation. In addition numerical simulations show, near the lock, an area in which the gravity current’s velocity is negative, i.e. the dense fluid is moving downslope.