Effect of effusion hole arrangement on jet array impingement heat transfer

Impingement/effusion cooling systems have been studied extensively over the past few decades to constantly improve cooling performance as the turbine inlet temperature of modern gas turbine engines has increased. However, a Nusselt number correlation is less developed for an impingement/effusion cooling system with effusion holes in its impingement plate than for jet array impingement without effusion holes. Moreover, Nusselt number correlations, available for a wide range of geometric and flow parameters with various hole arrangements, are sparse for gas-turbine casing cooling systems. Therefore, this study investigated the effects of these parameters on the flow and heat transfer characteristics of an impingement/effusion cooling system that uses a jet array of effusion holes to cool a gas-turbine casing. The circular holes in the parallel jet and impingement plates were arranged in five different hole arrangements. Air forced through holes in the jet plate struck the impingement plate then discharged through the effusion holes of the impingement plate. Three-dimensional simulations were performed to examine the effects of hole pitch, distance between the jet and impingement plates, ratio of total jet area to heat transfer area, and Reynolds number based on the jet hole diameter on impingement heat transfer. A total of 300 simulations were run for the five hole arrangements to obtain the local and average Nusselt numbers on the impingement plate. Our results show that the radial acceleration and turbulence near the impingement plate, and the length of the jet potential core strongly affect the impingement heat transfer. This study also evaluated previous Nusselt number correlations for jet array impingement. This paper presents a new correlation to predict the average Nusselt number of jet array impingement applicable to the five hole arrangements.