Investigation of the effect of confinement on the heat transfer to round impinging jets exiting a long pipe

Measurements were performed to characterize the effect that a confining plate had on the heat transfer produced by round turbulent impinging jets exiting a long pipe with Reynolds numbers of 17 000–28 000. It was found that the presence of the confining plate did not have a large impact on the heat transfer produced by the impinging jets with H/D ⩾ 1, but did for the jets with H/D ⩽ 0.5, reducing the local heat transfer in the region r/D ⩾ 1.5 by up to 50%. Measurements of the static and fluctuating wall pressure in the jets indicated that the turbulent fluctuations near the heat transfer surface were reduced in size and convected more slowly in this region for the confined jets with H/D ⩽ 0.5. The location of the decrease in the heat transfer and the fluctuating wall pressure in the confined jets shifted laterally outward as the nozzle-to-plate distance increased, and seemed to be associated with the flow reattaching to the confining plate.