BUOYANT-THERMOCAPILLARY INSTABILITIES IN MEDIUM-PRANDTL-NUMBER FLUID LAYERS SUBJECT TO A HORIZONTAL TEMPERATURE-GRADIENT

Coupled buoyant and thermocapillary instabilities in a fluid layer of infinite horizontal extent bounded below by a rigid plane and above by a free flat surface and submitted to a temperature gradient are investigated. A general 3D mathematical formulation is used to determine the linearized perturbated equations of the steady state induced by the temperature gradient. Numerical results are obtained in the case of a horizontal temperature gradient, lower and upper surfaces are adiabatically isolated and the range of variation of the Prandtl number is selected as [10(-2), 10]. The presence of travelling rolls is exhibited. The results display three kinds of behaviour according to the values taken by the Prandtl number: (a) 4 x 10(-3) < Pr < 0.4, (b) 0.4 < Pr < 2.6 and (c) Pr > 2.6.