NONLINEAR THERMAL CONVECTION IN AN ELASTIVISCOUS LAYER HEATED FROM BELOW.

The study of nonlinear effects for slightly supercritical Rayleigh number (which measures the temperature contrast across the layer) shows that plane disturbances for the case where the exchange of stability is valid and plane or centered disturbances for the case of overstability are governed by equations similar to those derived by Hocking, Stewartson & Stuart for plane Poiseuille flow. The influence of elasticity is to give rise to a burst only when the principle of exchange of stability is valid and provided certain conditions relating to the elastic parameters of the fluid are satisfied. The effect of the adiabatic temperature gradient is also discussed.