Impingement heat transfer on a target plate with film cooling holes
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Detailed heat-transfer distributions are presented for an array of jets impinging on a target plate with a staggered array of film cooling holes. The flow impinges on the target plate through a row of impingement holes and exits the channel from the sides and through the film holes. The top plate has 12 rows of impingement holes, and the target plate has 11 rows of film holes. The impingement holes and the film holes have the same diameter and are staggered such that the air from the impingement hole does not exit directly through the film hole. The setup is typical of an impingement/transpiration cooled gas turbine airfoil. Additional to the flow exiting through the film holes, there is an exit for crossflow after impingement. The exit opening of the impingement channel is changed to provide three different spent air exit directions. The detailed heat-transfer coefficient distributions were measured using a transient liquid crystal technique. Results are presented for a range of jet Reynolds numbers between 0.4103 and 2.0104 with different exit flow orientations. Heat-transfer results for the target plate with film holes are compared with those without film holes under the same flow conditions. Film extraction reduces crossflow effects on jet impingement heat transfer. However, overall averaged heat-transfer rates on the target surface appear less affected by presence of film hole for cases where the crossflow is generated in only one direction.
