Relation between the points of flow reattachment and maximum heat transfer for regions of flow separation

The streamwise distribution of the Nusselt number within and just downstream of a region of flow separation displays a maximum whose location, relative to the point of reattachment of the flow, was investigated here. Wind tunnel experiments were performed in which a circular cylinder was oriented longitudinal to a uniform freestream. Due to flow separation at the outer rim of the forward face of the cylinder, the upstream portion of the cylindrical surface was washed by a zone of recirculating fluid. Three configurations of the longitudinal cylinder were investigated : one with a solid, blunt forward face, a second with a hollow bore open at both its upstream and downstream ends, and a third in which the hollow bore was closed at its downstream end. The blunt-face case was also solved numerically. Additional numerical solutions were carried out for the contrastingly different case of an abrupt enlargement in a parallel-plate channel. Both the experimental and numerical results provided conclusive evidence that the commonly assumed equality of the points of flow reattachment and maximum heat transfer coefficient was, at best, a special case. For most of the cases investigated here, the heat transfer maximum occurred upstream of the reattachment point. Factors influencing the relative positions of the maximum and the reattachment were identified.