Rim Seal Experiments and Analysis for Turbine Applications

An experimental investigation was conducted to determine the sealing effectiveness and the aerodynamic characteristics of four rim seal models for a number of flow conditions. The experiments were conducted to obtain an extended data base for advanced turbine rim seal design. The class of rim seals investigated are those found on the downstream side of the rotor where the boundary layer on the disk is pumped directly into the seal gap. The experiments were conducted at disk tangential Reynolds numbers up to 5.1 × 10⁶ with a simulated gas path flow across the top of the seal. The simulated gas path flow was injected with various amounts of swirl to determine the effect of swirl on the seal effectiveness. The radial gap and the axial overlap of the seal were varied and results compared with a baseline configuration. A rim seal configuration intended to prevent disk pumping directly into the seal gap was also investigated. A mass transfer analogy was used to characterize the rim seal ingestion characteristics and the trace gas chosen for this technique was CO₂. The results of this investigation indicate that decreasing the radial gap of the seal produces a better improvement in seal effectiveness than increasing the axial overlap of the seal, that seal effectiveness increases only modestly as the swirl across the top of the seal decreases, and that the trace gas technique employed to determine seal effectiveness is an accurate alternative to pressure measurement or flow visualization techniques used by other investigators. The results of this investigation were compared with results from a boundary layer model for rim seals with axial gap geometries.