Flow and heat transfer measurements in a planar offset attaching jet with a co-flowing wall jet

Abstract

Measurements were performed to characterize the flow, mean skin friction, and heat transfer rate in flows consisting of a turbulent planar jet with Reynolds number of approximately 42,000 offset one jet height above a wall and a co-flowing wall jet with an initial height 0.18 times the offset distance (Hs). The results were compared to previous measurements for flows with similar offset jets and a co-flowing wall jet with initial height 0.5 times the offset distance. Low velocity wall jets in both geometries were quickly entrained into the offset jet increasing the attachment length of the offset jet and reducing the turbulent fluctuations and the heat transfer rate in the near field of the attaching jet. These changes increased with the mass flow rate of the wall jet as less mass is recirculated upstream from the attachment region. Higher velocity wall jets in both geometries initially remained attached to the wall causing a recirculation region to form between the jets that induce periodic motions that significantly increase the wall normal turbulent fluctuations in the flow. The periodic motions in the flows with the smaller wall jets significantly increased the pressure fluctuations on the wall below the near field flow and enhanced the heat transfer in this region. This differed from the results for the offset jet with the larger co-flowing wall jet where the flow fluctuations did not have a significant effect on the wall pressure fluctuations and the heat transfer below the flow. The difference in the effect of the periodic motions for flows appears to be due to differences in the forcing of the offset jet by the periodic motions and differences in the interaction between the recirculation region and the wall due to the height and mass flux of the wall jets.