Transient thermal structure, turbulence, and heat transfer in a reattaching slot jet flow

The role of turbulent fluctuations on mean heat transfer coefficient in a reattaching slot jet flow is studied experimentally. Convective heat transfer rate and near-wall fluid flow are examined in the recirculation, reattachment, and post-reattachment regions for two nozzle-to-surface spacings of 0.25 and 0.75 times the width of the nozzle bottom plate. In the reattachment region, results indicate a strong correspondence between variances of near-wall velocity fluctuation and peak heat transfer rate for both spacings. Thermal structures that vary in the spanwise direction are identified in the recirculation region from low-frequency transient infrared thermographs of the heated surface. While these thermal structures are confined to regions in the vicinity of nozzle bottom plate for the low nozzle spacing, they span the entire recirculation region at larger spacings. Thermal streaks are observed past reattachment for the larger nozzle spacing, suggesting a periodic breakup and re-formation of the jet curtain. The scaling of heat transfer distribution is affected by the flow structure in the geometrically non-similar area of the recirculating flow beneath the nozzle. A correlation for peak Nusselt number is presented.