Experimental Measurements of Ingestion Through Turbine Rim Seals: Part 3—Single and Double Seals

Abstract

This paper describes experimental results from a research facility which experimentally models hot gas ingress into the wheel-space of an axial turbine stage. Measurements of CO2 gas concentration in the rim-seal region and inside the wheel-space are used to assess the performance of generic (though engine-representative) single and double seals in terms of the variation of concentration effectiveness with sealing flow rate. The variation of pressure in the turbine annulus, which governs externally-induced ingress, was obtained from steady pressure measurements downstream of the vanes. The benefit of using double seals is demonstrated: the ingested gas is shown to be predominately confined to the outer wheel-space radially outward of the inner seal; in the inner wheel-space, radially inward of the inner seal, the effectiveness is shown to be significantly higher. Criteria for ranking the performance of single and double seals are proposed, and the performance limit for any double seal is shown to be one in which the inner seal is exposed to rotationally-induced ingress. Although the ingress is a consequence of an unsteady, three-dimensional flow field and the cause-effect relationship between pressure and the sealing effectiveness is complex, the experimental data is shown to be successfully calculated by simple effectiveness equations developed from a theoretical model. The data illustrate that, for similar turbine-stage velocity triangles, the effectiveness can be correlated using two empirical parameters. In principle, these correlations could be extrapolated to a geometrically-similar turbine operating at engine-representative conditions.

Experimental measurements of hot gas ingestion through turbine rim seals at off-design conditions

“…Again this is consistent with results presented in Sangan et al. 9 for EI ingress in double seals.

Figure 16.Variation of Φmin' with flow coefficient deduced from effectiveness curves for double seal. Solid and open symbols denote outer and inner seal respectively.

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The Design of a Steady Aero Thermal Research Turbine (START) for Studying Secondary Flow Leakages and Airfoil Heat Transfer

“…The Bath rotating turbine rig operates at steady state with vanes and partially-loaded blades. The Bath rig has allowed for a detailed study of many rim seal geometries [23] with optical access for thermal measurements on both the stationary and rotating sides of the cavity [24]. The Penn State low speed turbine rig is a large scale, low speed, cold flow rotating turbine facility.…”

Steady computations of ingress through gas turbine rim seals

“…This paper makes use of the measurements of Sangan et al 4,[14][15][16] , who conducted extensive experimental research related to hot gas ingress into the wheel-space of a simplified axial turbine stage. The test section of the facility, shown in Figure 4, features a turbine stage with 32 stator vanes and 41 symmetric NACA 0018 section rotor blades.…”