Numerical experiments of partial-depth colliding gravity currents using LES

The collision of two opposing, horizontal gravity currents is investigated numerically using Large Eddy Simulation (LES). The classical lock-exchange configuration is considered for symmetric collision (currents with same densities and heights). A partial-depth setup is used which is considered to simulate better the collision in deep air column of atmosphere. LES results are validated using available experimental and DNS data (Fragoso et al. in J Fluid Mech 734:1-10, https://doi.org/10.1017/jfm.2013.475; Frantz et al. in Comput Fluids, 2021. https://doi.org/10.1016/j.compfluid.2021.104902) for the classical full depth lock-exchange gravity current. Numerical experiments are performed considering the effects of D/H (D is the height of dense fluid in the lock, H is the tank height) and Grashof number (Gr) on the collision characteristics. The former varies from 0.25 to 1.0 and the latter from 106 to 1012. Maximum vertical displacement and maximum vertical velocity increase with decreasing D/H from 1.0 up to 0.5. They remain constant for D/H = 0.5. Maximum vertical displacement decreases with Gr number opposite to the corresponding variation of the maximum equivalent height. Maximum vertical velocity decreases with increasing Gr number, due to increased turbulence. For Gr = 5 x 108 (a) the maximum vertical displacement is almost constant (equal to 1.4D), (b) the temporal evolution of energies is approximately the same. At the time of maximum height the maximum potential energy and the minimum kinetic energy are approximately 80% and 15% of the initial potential energy, respectively, and (c) a region with intense turbulence and mixing of less dense fluid (C = 0.6, C is the concentration) is formed after the occurrence of maximum height in the middle of the domain.