Multiple-jet impingement heat transfer in double-wall cooling structures with pin fins and effusion holes

In a double-wall cooling system with multiple jet impingement the arrangement and size of effusion holes may change flow field and thereby change heat transfer characteristics. This paper stands in the view of internal cooling of turbine blades, and studied multiple-jet impingement heat transfer in double-wall cooling structures with narrow channels with pin fins and different-size effusion holes on the target wall. Five target plates were investigated including flat plate, pin fin plate and three pin fin plates with different-size effusion holes (effusion-to-jet diameter ratio of De/Dj=0.5,1.0and1.5). Transient liquid crystal thermography experiments were conducted to explore the heat transfer characteristics on these target plates. The ratio of jet-to-plate spacing was fixed to be 1.5 and Reynolds numbers based on the jet diameter range from 15,000 to 30,000. The experimental results showed that the pin fins and effusion holes reduce the crossflow strength in downstream region, improve and uniform heat transfer on the whole target plate obviously. Compared with the flat plate, pin fin plate with effusion holes of De/Dj=1.5 has highest averaged Nusselt number on the endwall. Numerical computations were carried out based on the experimental model, which revealed that the total heat transfer quantity on the pin fin plate with effusion holes of De/Dj=1.5 can be increased by up to 51% comparing to that of the flat plate. Detailed interactional flow information between the wall jet flow, pin fins and effusion holes is expounded for the heat transfer improvement in the impingement-effusion structures. Moreover, conjugate heat transfer analyses were done to further investigate the overall cooling performance of the impingement-effusion structures.