HIGH-REYNOLDS-NUMBER THERMAL TURBULENCE IN MERCURY

We have studied the scaling properties of turbulence in a Rayleigh-Ben ard convection cell. using a low-Prandtl-number (Pr) fluid. Hg (Pr=0.0 24). The length scales of thermal and viscous layers, analyzed from ti me series of movable thermistors near the cold upper plate, revealed t hat the viscous boundary layer is thinner than the thermal one over th e observed range of Rayleigh numbers (10(6) < Ra < 10(8)). This featur e, peculiar to low Pr fluid convection. differed from what is commonly observed in He. water, or other fluids. The scaling of Reynolds numbe r Re and Nusselt number Nu has been investigated using different aspec t ratio cells (Gamma = 0.5, 1, and 2) for a wider range of Ra. The hyp othetical ultimate regime (Nu similar to Ra-1/2) was not observed in t he range 10(5) < Ra < 2 x 10(9) even though the two boundary layers ar e inverted.