Buoyancy-induced flow occurs inside the rotating compressor cavities of gas turbines. These cavities are usually open at the inner radius, but in some industrial gas turbines, they are effectively closed. This paper presents measurements of the disk heat transfer and rotating flow structures in a closed cavity over a wide range of engine relevant conditions. These experimentally derived distributions of disk temperature and heat flux are the first of their kind to be published. The radial distribution of the nondimensional disk temperature virtually collapsed onto a single curve over the full experimental range. There was a small, monotonic departure from this common curve with increasing Reynolds number; this was attributed to compressibility effects where the core temperature increases as the rotational speed increases. These results imply that, if compressibility effects are negligible, all rotating closed cavities should have a disk temperature distribution uniquely related to the geometry and disk material; this is of important practical use to the engine designer. Unsteady pressure sensors detected either three or four vortex pairs across the experimental range. The number of pairs changed with Grashof number, and the structures slipped relative to the rotating disks by less than 1% of the disk speed.