Onset and non-linear regimes of convection of viscoelastic fluid in a square cavity heated from below

Stability of a conductive state and supercritical regimes of thermal buoyancy convection of Oldroyd-B viscoelastic fluid in a square cavity with adiabatic lateral walls heated from below is studied. The boundaries of linear stability of the conductive state to different instability modes are obtained by the direct numerical simulation of temporal evolution of perturbations based on non-stationary linearized equations for small perturbations. It is found that, at some values of rheological parameters, the bifurcation surfaces for perturbations of different spatial symmetries can intersect. The behavior of a system in the vicinity of intersections of bifurcation surfaces for the perturbations of different symmetries is investigated by means of direct numerical simulation based on a full nonlinear set of equations.