Effect of Jet-to-Plate Temperature Ratio on Flow and Heat Transfer Features of Active Clearance Control Systems

The goal of the present work is to investigate the effects of target plate temperature on heat transfer features of representative active clearance control (ACC) geometries presenting 0.8 mm circular impingement holes arranged in a single row pattern. The jets generated by such holes cool a flat target surface, which is replicated by a metal plate in the experimental setup. A steady-state technique with controlled wall heat flux is used to measure averaged heat transfer values along the target plate. The target plate is composed by a series of insulated blocks to limit lateral conduction effects and also to assure a fine control of the supplied power. A full characterization of pipe, target plate and flow temperature is obtained using thermocouples and IR camera. Target plate temperature level ranges from 330 K to 570 K, while the manifold inlet temperature is kept at ambient level. The jetto-target plate temperature ratio (TR) thus ranges from 1 to 2 circa. The investigated jet Reynolds numbers range from 4000 to 10000. The obtained results reveal that heat transfer features are affected by the target plate temperature level, as it plays a role on the interaction between the impingement jets, the spent flow and the manifold surfaces. An in-depth analysis of the obtained results provides valuable information about the extrapolation of ambient test results to engine conditions.