Conditioning of Leakage Flows in Gas Turbine Rotor-Stator Cavities

Ingress is the penetration of hot mainstream fluid into the cavity formed between the turbine disk (rotor) and its adjacent casing (stator). Gas turbine engine designers use rim-seals fitted at the periphery of the disks, and a superposed sealant flow-typically fed through the bore of the stator-is used to reduce, or in the limit prevent, ingress. Parasitic leakage enters the cavity through pathways created between mating interfaces of engine components. Owing to the aggressive thermal and centrifugal loading experienced during the turbine operating cycle, the degree of leakage and its effect on ingress are difficult to predict. This paper considers the potential for leakage flows to be conditioned in order to minimize their parasitic effect on disk cooling, and ultimately engine, performance. Measurements of static and total pressure, swirl, and species concentration were used to assess the performance of a simple axial clearance rim-seal over a range of nondimensional leakage flow rates. A computational model was used to provide flow visualization to support the interpretation of flow structures derived from the experiments. Data are presented to investigate the effects of swirling the leakage flow in accordance with, and counter to, the disk rotation. The injected momentum from the leakage created a toroidal vortex in the outer part of the cavity. Coswirl was found to improve the sealing effectiveness by up to 15% compared to the axially introduced baseline and counterswirled configurations. Varying the momentum of the leakage flow was considered by passing consistent mass-flows through a range of leakage outlet areas. Increasing the momentum was seen to increase the influence of the toroidal vortex on the flow structure in the cavity, which in turn influenced the sealing effectiveness.