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

Abstract

Abstract In order to produce efficient engines it is essential for gas tur-bine 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 an-nulus 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 (through reduced cooling). To ensure that this does not happen, contactless seals (rim 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 pri-marily due to the difference in kinematic (flow velocity and mass flow) and thermodynamic (density, enthalpy) properties of the two stream 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 (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 2.2 × 106 and axial Reynolds number of the order of 0.7 × 106, 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 typical mission profiles, cavity radial temperature distribution, and the measured cavity sealing effectiveness.