Effect of periodic unsteadiness on heat transfer in a turbulent boundary layer downstream of a cylinder-wall junction

Abstract

Abstract The heat transport and wall heat transfer in a turbulent boundary layer downstream of a cylinder-wall junction has been investigated experimentally. The heat transfer effect of local periodic, large-scale unsteadiness, as a result of vortex shedding from the cylinder, was examined using a conditional data-sampling and analysis technique that separated the large-scale periodic motion from the background turbulence. Detailed measurements of temperature and velocity were obtained using a cold wire and a custom-designed heat-flux probe. Thin-film, heat-flux surface sensors were used to obtain the time-resolved wall heat flux. Experiments were conducted approximately 5 diameters downstream of the leading edge of the cylinder, at Re D = 36,000 and Re L = 970,000. The boundary-layer transport and wall heat transfer were affected by the presence of large-scale periodic unsteadiness arising from vortex shedding in a region spanning approximately 2 diameters on either side of the cylinder. Large-scale fluctuations of the time-resolved wall-Stanton number were caused by the thinning and thickening of the near-wall thermal layer by periodic fluctuations in the vertical component of velocity.