Sealing and clearance control are two of the most cost effective methods to reach desired goals of efficiency, power output, operational life and emission levels in turbomachinery. Metallic seals such as W seals are widely used in gas turbines to seal axial gaps between adjacent static components such as shrouds and nozzles. Often the seals are characterized in a laboratory controlled environment, and the test results are used in modeling the secondary flows. However in real operating conditions, the static components can shift relative to each other creating misalignments that result in non-uniform sealing surfaces. One such application includes sealing between the stage 1 outer and inner shrouds. The inner shrouds are often stacked with axial misalignments relative to the neighboring shrouds due to manufacturing and assembly tolerances. Characterizing the effect of shroud misalignments on the W seal leakage is reported in this article. A comprehensive test matrix is conducted to characterize W seal leakage for four different magnitudes of shroud offsets, three types of seals having varying stiffness, and two compression levels. It is observed that the W seal leakage is fairly insensitive to the compression levels and the type of seal at zero misalignments. The seal leakage increases substantially with misalignments up to four times than for a perfectly aligned condition. The seal behavior also changes with increasing offsets. The seal exhibits typical properties of a positively loaded member for small misalignments, however, the behavior resembles a loose seal for larger misalignments. For a positively loaded seal, the effective clearance of the seal increases with pressure differential, whereas in case of a loose seal, the effective clearance decreases with increasing pressure differential. The effect of misalignments must be considered when modeling the seal in the engine flow models using a weighted average of the effective clearance.
Characterization of Metallic W-Seals for Inner to Outer Shroud Sealing in Industrial Gas Turbines
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Sarawate, N, Wolfe, C, Sezer, I, Ziegler, R, & Chupp, R. "Characterization of Metallic W-Seals for Inner to Outer Shroud Sealing in Industrial Gas Turbines." Proceedings of the ASME Turbo Expo 2012: Turbine Technical Conference and Exposition. Volume 4: Heat Transfer, Parts A and B. Copenhagen, Denmark. June 11–15, 2012. pp. 1855-1862. ASME. https://doi.org/10.1115/GT2012-68131
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