Local heat transfer rates from two adjacent spheres in turbulent axisymmetric flow

The flow interactions between two spheres in a turbulent air stream was studied in a vertical wind tunnel. The flow Reynolds number was approximately 10,000 with a turbulence intensity of 1.1 percent and the spacing between the spheres was varied from 5.6 to 1.04 diameters. Both the local surface pressures and the local heat transfer coefficients were measured. Moreover, the experimental technique used allowed both the steady and the fluctuating components of the heat transfer to be measured. At wide spacings, the drag on the trailing sphere was larger than that on a single sphere. At spacing closer than 2.2 diameters, the wake of the leading sphere consisted of vortex rings attached to both spheres. These caused an increase in the heat transfer from both spheres and a substantial decrease in the drag on the trailing sphere.