Numerical investigation of jet array impingement cooling with effusion holes

•Heat transfer characteristics of jet array impingement with effusion holes are examined.•A wide range of geometrical and flow parameters are numerically investigated.•The length of jet potential core has a significant effect on flow structure and heat transfer.•A new correlation for predicting the average Nusselt number is proposed. Although impingement/effusion cooling systems have been extensively studied over the past several decades, studies on flow and heat transfer characteristics over a wide range of geometrical and flow parameters are still lacking. Moreover, most studies have been related to gas-turbine blade cooling, and only a few studies have focused on gas-turbine casing cooling. In addition, studies that attempted to develop a Nusselt number correlation for jet array impingement with effusion holes––where these holes are installed in the impingement plate––are scarce. This study primarily aimed to explore the heat transfer characteristics of jet array impingement with effusion holes and to provide basic data for the design of a gas-turbine casing cooling system. Perforated circular holes in two parallel plates were arranged in a staggered configuration. The air injected through the jet holes impacts the impingement plate, and the spent air from the impinging jets is then discharged through the effusion holes in the impingement plate. A three-dimensional numerical unit cell model was constructed to investigate the effect of the hole pitch, distance between the jet plate and the impingement plate, Reynolds number based on the hole diameter, and hole diameter on the impingement heat transfer. The numerical model was validated by comparing its numerical predictions for a wide range of geometric parameters using previous experimental data. The local and average Nusselt numbers on the impingement plane were obtained for 74 simulation cases, and the results show that the jet potential core has a significant influence on the flow structure and heat transfer in a confined jet impingement. The accuracy of previous Nusselt number correlations for a jet array impingement was assessed, and we proposed a new correlation for predicting the average Nusselt number for a jet array impingement with effusion holes.