For producing efficient engines it is essential for gas turbine designers to understand the interaction between the primary and secondary air systems in critical parts of the engine. One of these is the first stage turbine, where the ingress of the hot annulus air into the rotor stator cavity could be catastrophic due to the increased heat load on the disc posts and on the rotor blades themselves. To ensure that this does not happen, contactless seals are built into the outer radius of the rotating disc. Additionally, a secondary air flow rate must be appropriately set in order to ‘purge’ the hot air that could be ingested into the rim seal cavity. However, this purge airflow could cause deterioration of the turbine performance as it re-joins the main annulus flow at the interface between the rim seal cavity and the main annulus. The deterioration in performance is primarily due to the difference in kinematic and thermodynamic properties of the two streams of air. It is therefore essential to understand the optimum seal geometry and purge flow rates required to prevent the ingestion of the hot annulus air while maintaining the required turbine performance. In this paper we present experimental test results from a single stage turbine facility, the Rim Seal Ingestion (RiSe) rig, at the University of Sussex. The turbine stage incorporates a model rotor-stator cavity system that is representative of the first stage turbine in a gas turbine engine. The facility is capable of generating disc cavity rotational Reynolds numbers of the order of 2 x 10^6^ and stator chord based main flow Reynolds number of the order of 1 x 10^6^, while operating at a pressure ratio of 2.5. The paper will present the salient features of the test facility, the various instrumentation employed, and the operating specifications of the stage. The paper will discuss the effect of varying the purge flow for a fixed operating point of the turbine. Results presented will include the measured cavity sealing effectiveness estimated using both disc surface temperature measurements and gas concentration measurements using CO2 as tracer gas. The effect of the purge air on the main flow will be presented using temperature, pressure and gas concentration measurements made in the annulus region. Of particular interest will be the blade surface temperature measurement from the rotor blades captured using a telemetry based measuring system. The paper will be concluded with a brief discussion of the overall effect of the purge flow variation on the performance of the turbine stage.


Experimental Investigation on the Effect of Varying Purge Flow in a Newly Commissioned Single Stage Turbine Test Facility

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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