Performance of a Turbine Rim Seal Subject to Rotationally-Driven and Pressure-Driven Ingestion

Abstract

This experimental study considered the performance of a chute rim seal downstream of turbine nozzle guide vanes (but without rotor blades). The experimental setup reproduced rotationally-driven ingestion without vanes and conditions of pressure-driven ingestion with vanes. The maximum rotor speed was 9000 rpm corresponding to a rotational Reynolds number of 3.3 × 106 with a flow coefficient of 0.45. Measurements of mean pressures in the annulus and the disk rim cavity as well as values of sealing effectiveness deduced from gas concentration data are presented. At high values of flow coefficient (low rotational speeds), the circumferential pressure variation generated by the vanes drove relatively high levels of ingestion into the disk rim cavity. For a given purge flow rate, increasing the disk rotational speed led to a reduction in ingestion, shown by higher values of sealing effectiveness, despite the presence of upstream vanes. At Uax/(Ωb)=0.45, the sealing effectiveness approached that associated with purely rotationally-driven ingestion. A map of sealing effectiveness against non-dimensional purge flow summarizes the results and illustrates the combined rotational and pressure-driven effects on the ingestion mechanism. The results imply that flow coefficient is a relevant parameter in rim sealing and that rotational effects are important in many applications, especially turbines with low flow coefficient.