LAUSR

Abstract This study aims at investigating numerically the Rayleigh-Benard Convection (RBC) in viscoplastic fluids. A Casson fluid is considered in a bidimensional square cavity heated from below. The effects of the dimensionless yield stress, the Bingham number B n , on the heat transfer and motion is investigated in the range 5.10 3 R a 10 5 for the Rayleigh number and P r = 10 , 100 , 1000 for the Prandtl number. One shows that the yield stress has a stabilizing effect, reducing the convection intensity. Above a certain value of B n m a x , the convection does not occur and the heat transfer is only due to conduction. For moderate B n values, truly unyielded regions are located in the center of the cavity; their areas grow with increasing Bingham number and invade the whole cavity at the threshold value B n m a x .