Jet Impingement Heat Transfer Enhancement by U-Shaped Crossflow Diverters

Abstract

Array-jet impingement is typically used in gas turbine blade near-wall cooling, where high rates of heat dissipation is required. The accumulated crossflow mass flux results in significant reduction in jet effectiveness in the downstream rows, leading to reduced cooling performance. In this paper, a jet impingement system equipped with U-shaped ribs (hereafter referred as “diverter”) was used for diverting the crossflow away from the jets emanating from the nozzle plate. To this end, a baseline configuration of array-jet impingement onto smooth target surface is considered, where the normalized jet-to-jet spacing (x/dj = y/dj) was 6 and the normalized jet-to-target spacing (z/dj) was 2. Crossflow diverters with thickness t of 1.5875 mm and height h of 2dj (= z) were installed at a distance of 2dj from the respective jet centers. Detailed heat transfer coefficients have been calculated through transient liquid crystal experiments carried out over Reynolds numbers ranging from 3500 to 12,000. It has been observed that crossflow diverters protect the downstream jets from upstream jet deflection, thereby maximizing their stagnation cooling potential. An average of 15–30% enhancement in Nusselt number is obtained over the flow range tested. This benefit in heat transfer came at a cost of increased pumping power to maintain similar flow rate in the system. At a given pumping power, crossflow diverters yielded an enhancement of 9–15% in heat transfer compared with the baseline case.