CONVECTION UNDER ROTATION FOR PRANDTL NUMBERS NEAR-1 - LINEAR-STABILITY, WAVE-NUMBER SELECTION, AND PATTERN DYNAMICS

Rayleigh-Benard convection with rotation about a vertical axis was stu died with the shadowgraph imaging method up to a dimensionless rotatio n rate Omega of 22. Most of the results are for a cylindrical convecti on cell with a radius-to-height ratio Gamma = 40 that contained CO2 at 33.1 bars with a Prandtl number sigma = 0.93. Measurements of the cri tical Rayleigh number R-c and wave number k(c) for 0 < Omega < 22 agre e well with predictions based on linear stability analysis. Above onse t and with rotation, the average wave number and details of the patter n dynamics were studied. For Omega less than or similar to 5, the init ial onset was to a pattern of straight or slightly curved rolls. For 0 .1 less than or similar to epsilon = Delta T/Delta T-c - 1 less than o r similar to 0.5 but below the onset of spiral-defect chaos, rotation with Omega less than or similar to 8 produced weak perturbations of no nrotating patterns. Typically, this gave an ''S-shaped'' distortion of the zero-rotation pattern of straight or somewhat curved rolls. Rotat ion had a stronger effect on thr source and motions of dislocation def ects. For Omega > 0 the defects were generated primarily at the wall, whereas for Omega = 0 they were nucleated in the bulk via the skewed-v aricose instability. Rotation picked a preferred direction of motion f or the defects once they formed. For epsilon greater than or similar t o 0.5, recognizable spiral-defect chaos and the oscillatory instabilit y were observed for Omega less than or similar to 12. For Omega greate r than or equal to 8, domain growth and front propagation suggestive o f the Kuppers-Lortz instability were observed from onset up to an epsi lon value that increased with Omega. Increasing epsilon at fixed Omega less than or similar to 12 enhanced dislocation-defect dynamics over Kuppers-Lortz front propagation. Quantitative measurements of average pattern wave numbers, correlation lengths, and spatially averaged roll curvature as functions of epsilon and R are presented, At a fixed Ome ga greater than or similar to 10, the average wave number had two dist inct wave-number-selection regions with different slopes as a function of epsilon, one above epsilon approximate to 0.45 and thr other near onset. The slope for epsilon near onset reached a minimum Omega = 12.1 and increased Linearly for 12 < Omega < 20.