Heat Transfer Coefficients and Patterns of Fluid Flow for Contacting Spheres at Various Angles of Attack

Wind tunnel experiments were performed to determine heat transfer coefficients and fluid flow patterns for two contacting spheres. The experiments were carried out at three different angles of attack and for Reynolds numbers in the range from 4000 to 26,000. Three heat transfer conditions were considered: (a) both spheres thermally active, (b) forwardmost sphere thermally active and rearmost sphere adiabatic, and (c) forwardmost sphere adiabatic and rearmost sphere thermally active. Complementary experiments for a single sphere, encompassing the same parameter ranges, yielded baseline information for comparison with the two-sphere results. It was found that the largest effects of the sphere-to-sphere interaction on the heat transfer occurred when the two spheres were in line. At this orientation and for higher Reynolds numbers in the investigated range, there was substantial enhancement of the heat transfer with respect to that for the single sphere. At the other angles of attack, there was lesser enhancement. The visualization studies revealed such key fluid flow features as the reattachment of the separated flow from the first sphere on the second, the presence of strong recirculations, and the delay of separation due to pressure-driven transverse flows.