Pressure Activated Leaf Seal Technology Readiness Testing

Abstract

This paper continues the evaluation of Pressure Actuated Leaf Seals (PALS) 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 (129.54mm) diameter smooth surface test rotor and another that simulates sealing against turbine blade shrouds. A further test was undertaken using a 2D static rig that determined acoustic noise experienced during testing was attributed to leaves vibrating at their natural frequency as a result of inter-leaf 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 hours 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 0.010in (0.25mm) against rotor discs 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.

Film Riding Pressure Activated Leaf Seal Proof of Concept

“…Advancing from the PALS concept [7] , the evolution to the FRPALS was first introduced in 2010 [1] (Figure 1). This hydrostatic compliant seal uses the PALS concept of deflecting leaves that actuate under pressure loading to close down to the rotor under the desired operating conditions, while maintaining a large clearance at start/stop conditions.…”