Special characteristics of a double-diffusive instability found in oceans

The evolution of horizontal double-diffusive layers (DDLs) is one of the outcomes of double-diffusive convection found in many natural and industrial transport processes e.g., DDLs in oceans, earth's mantle, solar ponds etc. A CFD based fluent model is developed for the investigation of different characteristics of the onset, sustenance, merging and disappearance of DDLs by imposing lateral thermal gradients in a stably stratified compositional field. A specially oriented large-scale convection roll was found inside each DDL and each roll was driven by the competing density change due to pre-existing compositional and imposed thermal field. Various combinations of solutal and thermal Rayleigh numbers were investigated to study different flow regimes and the effect on the number, width and time of sustenance of DDLs. A merging mechanism has been explained along with the special characteristics of sudden drop and rise of heat transfer coefficients on the sidewalls and average velocity in the whole domain. The present study is expected to be useful in correlating double-diffusive convection in many large-scale applications including oceanography, metallurgy, geology, etc. The model was also developed for 3-D geometry and the results were quite similar to that of 2-D simulations.