Heat Transfer in Separated Flow behind a Circular Cylinder for Reynolds Numbers from 120 to 30 000∗ (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 30 000. 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 6 000, 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.