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

Abstract

This paper describes experimental results from a research facility, which experimentally models hot gas ingress into the wheelspace of an axial turbine stage. Measurements of CO2 gas concentration in the rimseal region and inside the wheelspace are used to assess the performance of generic (though enginerepresentative) 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 wheelspace radially outward of the inner seal; and in the inner wheelspace, 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, threedimensional flow field and the causeeffect 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 turbinestage 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 enginerepresentative conditions.