Experimental Measurements of Ingestion Through Turbine Rim Seals—Part I: Externally Induced Ingress

Abstract

This paper describes a new research facility which experimentally models hot gas ingestion into the wheelspace of an axial turbine stage. Measurements of the CO2 gas concentration in the rimseal region and inside the cavity are used to assess the performance of two generic (though enginerepresentative) rimseal geometries in terms of the variation of concentration effectiveness with sealing flow rate. The variation of pressure in the turbine annulus, which governs this externallyinduced (EI) ingestion, was obtained from steady pressure measurements downstream of the vanes and near the rim seal upstream of the rotating blades. Although the ingestion through the rim seal is a consequence of an unsteady, threedimensional flow field and the causeeffect relationship between the pressure and the sealing effectiveness is complex, the experimental data is shown to be successfully calculated by simple effectiveness equations developed from a previously published orifice model. The data illustrate that, for similar turbinestage velocity triangles, the effectiveness can be correlated using a nondimensional sealing parameter, خ¦o. In principle, and within the limits of dimensional similitude, these correlations should apply to a geometricallysimilar engine at the same operating conditions. Part II of this paper describes an experimental investigation of rotationallyinduced (RI) ingress, where there is no mainstream flow and consequently no circumferential variation of external pressure.