Jet impingement heat transfer over surfaces with transverse high ribs at low Reynolds numbers pertinent to aeroengine ACC system

Abstract

The Active Clearance Control (ACC) system utilizes multiple jet impingement to cool the turbine casing of aero engines, aiming to reduce the tip clearance through thermal contraction. This study models the flange structures at the external turbine casing as transverse high ribs, and the performance of ACC configurations are compared on baseline ‘I’-shaped smooth surface, the ‘L’-shaped high rib surface, and the ‘U’-shaped high rib surface. Experimental study and numerical simulation are carried out to obtain the flow and heat transfer characteristics. The results indicate that the arrangement of transverse high ribs on the target surface significantly influences the flow and heat transfer characteristics. The heat transfer on the high rib is lowered by 23.5 % and 15.5 % on Geometry L and U compared to baseline flat surface, respectively, while the heat transfer on the bottom surface is slightly affected. Based on numerical results, the total heat transfer increases by up to 6.74 % and 122 % on Geometry L and U due to extended wetted area, respectively. As the separation distance elevates, the Nusselt number on the bottom surface reduces by 15.6 % and 20.2 % for Geometry L and U, while the Nusselt number on the high rib increased by 0.5 % and 8.5 %, respectively. The Geometry U has more uniform heat transfer distributions, especially at high separation distances. The discharge coefficients of Geometry I and L are similar for using the same manifolds, and the discharge coefficient of Geometry U is 4.7 % higher for larger outlet to inlet area ratio. Based on the experimental data, Nusselt number correlations of the jet impingement over the total surfaces with different high ribs is developed over low Reynolds number ranging from 1,000 to 10,000, which provide more accurate heat transfer predictions than peer works.