Direct numerical simulation of layer merging in a salt-stratified system

Time-dependent double-diffusive convection was studied numerically to clari fy the mechanism of layer merging in a salt-stratified system. Using the Ch ebyshev collocation method, a typical example of stably stratified salt flu id subject to a lateral temperature difference in a rectangular enclosure ( Ar = 1.25) is considered for realistic values of parameters (Ra-T = 2.7 X 1 0(7), N-i = 0.882, Pr = 7.15, and Sc = 685). Two cases that differ by the i nitial salt concentration profile, i.e., linear and steplike profiles, are examined. Although globally, in both cases, the layer merging process is ch aracterized by the mass transfer across the interface separating two convec tion layers, the two instances are quite different with respect to the inte rface structure. For the linear profile, vertical motion due to salt finger s is dominant, whereas for the steplike profile horizontal motion due to st rong shear flows prevails. In particular, in the latter case, unlike for th e linear profile case, traveling plumes perpendicular to shear flows that l ead to the time variations in temperature and concentration are periodicall y generated within the interface. Predictions obtained with the simulations are in good agreement with experimental data.