The retrograde propagation mechanism of critical thermal convection with a sectorial pattern emerging in a slowly rotating spherical shell is investigated through vorticity budget analysis. In the equatorial region, stretching and shrinking of the fluid columns in the direction of the axis of rotation due to the radial component of velocity causes retrograde propagation, whereas in the mid-latitudes, tilting of the radial component of planetary vorticity by the radial shear of the latitudinal component of velocity is dominant. The switching of the propagating direction from retrograde to prograde according to the increase in the rotation speed of the shell originates from the transition of the morphology of vortices from the ‘banana-shaped’ type due to the constraint of the spherical geometry to the columnar type due to the Taylor–Proudman constraint. The variation of the morphology of vortices reverses the tendency of stretching/shrinking of fluid columns accompanied by their cylindrically radial displacement.

Results are presented on the flow field downstream of a body of revolution for Reynolds numbers based on a model length ranging from 1.1 × 106 to 67 × 106. The maximum Reynolds number is more than an order of magnitude larger than that obtained in previous laboratory wake studies. Measurements are taken in the intermediate wake at locations 3, 6, 9, 12 and 15 diameters downstream from the stern in the midline plane. The model is based on an idealized submarine shape (DARPA SUBOFF), and it is mounted in a wind tunnel on a support shaped like a semi-infinite sail. The mean velocity distributions on the side opposite the support demonstrate self-similarity at all locations and Reynolds numbers, whereas the mean velocity distribution on the side of the support displays significant effects of the support wake. None of the Reynolds stress distributions of the flow attain self-similarity, and for all except the lowest Reynolds number, the support introduces a significant asymmetry into the wake which results in a decrease in the radial and streamwise turbulence intensities on the support side. The distributions continue to evolve with downstream position and Reynolds number, although a slow approach to the expected asymptotic behaviour is observed with increasing distance downstream.