The use of Brush Seals continues to expand in both the Power Generation and the Aerospace markets and we continue to learn more about their functionality. This paper continues on from our previous papers and in particular AIAA 2002-3794 which examines, analytically and experimentally the effects of Hysteresis. The 3D Finite Element Model has been developed further to more accurately predict the physics of brush seal hysteresis. This will be demonstrated by comparison of data from the model to test data gathered from manufactured seals tested in the laboratory. This model has full bristle-to-bristle contact, bristle to back plate contact, bristle to rotor contact and can be pressure drop loaded.

The industry bristle material of choice for brush seals has been the cobalt-based alloy Haynes®25 (also known as L605) for over 30 years. Haynes®25 has excellent oxidation resistance and wear properties in brush seal applications up to temperature of 620°C [1148°F]. Above this temperature creep resistance becomes undesirable for brush seal bristles and has lead to alternative sealing solutions to be implemented in these turbine locations. Nickel-based alloys have been explored as an alternative for Haynes®25 but have been shown to gall badly and wear quickly in comparison. As increases in turbine performance have resulted in an increase in operating temperatures, it has lead to a need to find a bristle material that performs at temperatures above the limitation of Haynes®25. Initial experimental data has been obtained for a new cobalt-based alloy that shows potential for use as a bristle material at temperatures above 620°C [1148°F]. Further experimental results also indicate that the material appears to have better wear characteristics than Haynes®25 and may prove to be a feasible alternative in some cases. This paper outlines a material selection process for brush seals, along with development of the alloy for use within brush seals and details of the comparative testing carried out at Cross Manufacturing Company.

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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.

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.