Pressure Activated Leaf Seal Technology Readiness Testing

This paper continues the evaluation of pressure actuated leaf seals (PALSs) technology readiness for shaft and shroud sealing in power generation and aerospace applications. Seal designs tested are prototypical and constructed using processes appropriate for volume production. Results include both static and dynamic seal leakage measurements running against a 5.1 in. (130 mm) diameter smooth surface test rotor and another that simulates sealing against turbine blade shrouds. A further test was undertaken using a two-dimensional (2D) static rig that determined acoustic noise experienced during testing was attributed to leaves vibrating at their natural frequency as a result of interleaf gaps. The dynamic simulated shroud test includes steps, duplicating small discontinuities of adjacent shroud sealing surfaces and slots to inject air radially under the seal leaves as may occur between shrouds on blades with a high degree of reaction. Consistent seal performance over 15 h confirms suitability for turbine blade tip applications. Controlled deflection of PALS leaves with operating differential pressure is effective for startup rub avoidance in service as well as conformal wear-in sizing of leaf tips with the rotor. Tested leaf tip wear-in of approximately 0.010 in. (0.25 mm) against rotor disks without hard-face coating shows potential to eliminate seal misalignment and run-out contributions to operating seal clearance. PALS design features prevent further rubbing contact with the operating rotor after initial wear-in sizing, thereby sustaining a small effective seal clearance and prospects for long seal life. Measurements of rotor surface wear tracks from the wear-in process and endurance runs are included as well as rotor and leaf tip photos. Test results support the technology readiness of the PALS concept as a viable, robust, low leakage dynamic seal for select commercial application.