CONVECTION AT VERY LOW PRANDTL NUMBERS

The transition from thermal convection in the form of rolls in a fluid layer heated from below to traveling wave convection occurs at the Rayleigh number RII = 1854 in the limit of low Prandtl numbers and in the presence of no-slip boundaries. While the traveling wave convection exhibits similar properties at moderately low and very low Prandtl numbers, the tertiary transition to asymmetric waves experiences a qualitative change at a Prandtl number of about 0.02. Instead of the double frequency asymmetric waves that occur at higher Prandtl numbers the traveling wave convection becomes just asymmetric, but remains stationary with respect to the moving frame of reference. The heat transport carried by the new form of convection is larger than for symmetric traveling wave convection. © 1990 American Institute of Physics.