Rayleigh-Bénard convection with rotation about a vertical axis was studied with the shadowgraph imaging method up to a dimensionless rotation rate Ω of 22. Most of the results are for a cylindrical convection cell with a radius-to-height ratio Γ=40 that contained ${\mathrm{CO}}_2$ at 33.1 bars with a Prandtl number σ=0.93. Measurements of the critical Rayleigh number ${\mathrm{R}}_{\mathrm{c}}$ and wave number ${\mathrm{k}}_{\mathrm{c}}$ for 0<Ω<22 agree well with predictions based on linear stability analysis. Above onset and with rotation, the average wave number and details of the pattern dynamics were studied. For Ω≲5, the initial onset was to a pattern of straight or slightly curved rolls. For 0.1≲ε≡ΔT/Δ${\mathrm{T}}_{\mathrm{c}}$-1≲0.5 but below the onset of spiral-defect chaos, rotation with Ω≲8 produced weak perturbations of nonrotating patterns. Typically, this gave an ``S-shaped'' distortion of the zero-rotation pattern of straight or somewhat curved rolls. Rotation had a stronger effect on the source and motions of dislocation defects. For Ω>0 the defects were generated primarily at the wall, whereas for Ω=0 they were nucleated in the bulk via the skewed-varicose instability. Rotation picked a preferred direction of motion for the defects once they formed. For ε≳0.5, recognizable spiral-defect chaos and the oscillatory instability were observed for Ω≲12. For Ω⩾8, domain growth and front propagation suggestive of the Küppers-Lortz instability were observed from onset up to an ε value that increased with Ω. Increasing ε at fixed Ω≲12 enhanced dislocation-defect dynamics over Küppers-Lortz front propagation. Quantitative measurements of average pattern wave numbers, correlation lengths, and spatially averaged roll curvature as functions of ε and Ω are presented. At a fixed Ω≳10, the average wave number had two distinct wave-number-selection regions with different slopes as a function of ε, one above ε≈0.45 and the other near onset. The slope for ε near onset reached a minimum at Ω=12.1 and increased linearly for 12<Ω<20.

DOI:https://doi.org/10.1103/PhysRevE.55.6928