A Comparison of Single-Entry and Multiple-Entry Casing Impingement Manifolds for Active Thermal Tip Clearance Control

In this paper, we investigate the aerothermal performance of active clearance control (ACC) methods that use impingement as a means of enhancing heat transfer. We describe a numerical approach to compare the aerothermal performance of two circumferential impingement manifold supply designs that vary in the number of entry points to the manifold channel. For a 180°-sector, the first design has a single entry point, while the second has two. Both the single-entry and multiple-entry systems analysed in this paper are idealised version of ACC systems in current production engines. Aerothermal performance is quantitatively assessed on the basis of the HTC distribution, driving temperature difference for heat transfer between the jet and casing wall, and total pressure loss within the HPT ACC system. We conclude key advantages and disadvantages of each system based on the impact on engine efficiency, response time, ease of optimisation and implications for weight, cost and complexity of the design.