Heat Transfer in Separated Flow behind a Circular Cylinder for Reynolds Numbers from 120 to 30000 : 2nd Report, Unsteady and Three-Dimensional Characteristics

This paper describes the unsteady and three-dimensional characteristics of heat transfer from a circular cylinder to the cross-flow of air for Reynolds numbers from 120 to 30000. An infrared camera was used to measure the time-spatial characteristics of heat transfer on the cylinder surface, heated under a condition of constant heat flux. Fluctuating heat transfer was measured using a heat flux sensor. The heat transfer in the separated flow region had a spanwise nonuniformity, the wavelength of which agreed well with that of the streamwise vortices formed in the near-wake. In particular, the streamwise vortices formed at approximately Re=200 due to "mode-A" instability effectively enhanced the heat transfer at the rear of the cylinder. For Reynolds numbers greater than 6000, the heat transfer at the rear face was markedly increased by the alternating reattaching flow, caused by the rolling-up of the separated shear layers.