Numerical aspects of the simulation of discontinuous saline underflows: the lock-exchange problem

Abstract

Issues associated with the adequate representation of flow instabilities of saline, discontinuous density currents in two and three dimensions are discussed. First, simulations of the experiments by Alahyari and Longmire (1996) developed with an advanced commercial code are presented, and they are compared with results obtained through Direct Numerical Simulation of the problem. Various meshes and turbulence models are then tested with the commercial code, including a Large Eddy Simulation. The features of the density current that are not reproduced well by the simulations with the commercial code are further analyzed. Then, two-dimensional numerical simulations of an unpublished set of experiments are presented. The response of commercial and open-source codes to different grids is addressed. Important conclusions on the risks of using inadequate resolution with codes in which not all variables are controlled are obtained, and the nature of these two-dimensional, “mathematical” numerical solutions is discussed.

Keywords:

• Computational fluid dynamics
• Dense underflows
• Density currents
• Lock-exchange flows
• Navier-Stokes equations