Natural doubly diffusive convection in three-dimensional enclosures

Numerical continuation is used to study bifurcations in doubly diffusive convection in three-dimensional enclosures driven by opposing horizontal temperature and concentration gradients, and the results are compared with the two-dimensional case. Direct numerical simulation is used to show that in certain regimes the first stable nontrivial state of the three-dimensional system is a finite amplitude nonlinear oscillation. This state may be either periodic or chaotic. The mechanism responsible for these oscillations is identified, and the oscillations shown to be an indirect consequence of the presence of a steady-state bifurcation to fundamentally three-dimensional longitudinal structures that are absent from a two-dimensional formulation. The role of global bifurcations in generating the chaotic oscillations is elucidated. (C) 2002 American Institute of Physics.