Abstract:
Double diffusive convection (DDC) is the buoyancy-driven flow, with density depend
ing on two different diffusing scalar components, distributed such that faster diffusing
component gravitationally stabilise the fluid and slower one destabilise it. The presence
of DDC is universal from oceans to stars. In oceans the two components heat and salt
are convected from top to depths of oceans affecting the climate of earth and life in
deep sea. The stable stratification of molten constituents in the interiors of planets and
gases in stars is disturbed due to this instability, reducing the background gradients
to change their internal structure. Our study involves numerical solutions of transient
Navier-Stokes equations by Finite Volume Method using SIMPLER algorithm. Majority
of our work is done at wide range of diffusivity ratio, density ratio and Rayleigh numbers
employing 2D model. For 3D model, a new 3D code was developed, and the effect of
Rayleigh number and density ratio is studied on the evolution of DDC system. To ex
pedite the increased size of 3D problem, parallelisation was done in one direction using
OpenMP. The results show that initial growth of fingers is arrested by density inversion.
Rayleigh number has strong effect, as compared to density ratio and diffusivity ratio, on
the scale of fingers and magnitude of constituents fluxes. At different values of Rayleigh
number and density ratio variety of planforms are observed. The formation of diffusive
staircases in 3D case at low density ratio is unlike its 2D counterpart, where constituents
spread uniformly without any hint of vertical layers.
The purpose of this thesis is to examine the salt finger morphology and mixing charac
teristics of double diffusive convection (DDC) for variety of fluids.
