Yuan-Ming Liu

Heat transport measurements in turbulent rotating Rayleigh-Bénard convection

We present experimental heat transport measurements of turbulent Rayleigh-Bénard convection with rotation about a vertical axis. The fluid, water with a Prandtl number (sigma) of about 6, was confined in a cell with a square cross section of 7.3 x 7.3 cm2 and a height of 9.4 cm. Heat transport was measured for Rayleigh numbers 2 x 10(5)<Ra<5 x 10(8) and Taylor numbers 0<Ta<5 x 10(9). We show the variation in normalized heat transport, the Nusselt number, at fixed dimensional rotation rate OmegaD, at fixed Ra varying Ta, at fixed Ta varying Ra, and at fixed Rossby number Ro. The scaling of heat transport in the range of 10(7) to about 10(9) is roughly 0.29 with a Ro-dependent coefficient or equivalently is also well fit by a combination of power laws of the form a Ra1/5+b Ra1/3. The range of Ra is not sufficient to differentiate single power law or combined power-law scaling. The data are roughly consistent with an assumption that the enhancement of heat transport owing to rotation is proportional to the number of vortical structures penetrating the boundary layer. We also compare indirect measures of thermal and Ekman boundary layer thicknesses to assess their potential role in controlling heat transport in different regimes of Ra and Ta.

Traveling-wave and vortex states in rotating Rayleigh–Bénard convection

Abstract Experimental results on states of rotating Rayleigh–Benard convection in water with a Prandtl number of 6.4 are presented. Using precision heat transport measurements and optical shadowgraph imaging, we have explored the sidewall traveling-wave state in cylindrical convection cells with radius-to-height ratios Γ =1, 2.5, and 5. The critical Rayleigh number and precession frequencies for the wall mode were measured as a function of a dimensionless rotation rate and are compared to theoretical predictions. The onset of bulk convection and its pattern wave number are found to agree quite closely with predictions of Chandrasekhar’s linear stability analysis. Vortex states at higher Rayleigh number are also described and characteristics of the thermal vortices including the vortex circulation and the frequency of collective vortex motions are presented.