Re-Ingestion of Upstream Egress in a 1.5-Stage Gas Turbine Rig

Abstract

In gas turbines, rim seals are fitted at the periphery of stator and rotor discs to minimize the purge flow required to seal the wheel-space between the discs. Ingestion (or ingress) of hot mainstream gases through rim seals is a threat to the operating life and integrity of highly stressed components, particularly in the first-stage turbine. Egress of sealing flow from the first-stage can be re-ingested in downstream stages. This paper presents experimental results using a 1.5-stage test facility designed to investigate ingress into the wheel-spaces upstream and downstream of a rotor disk. Re-ingestion was quantified using measurements of CO2 concentration, with seeding injected into the upstream and downstream sealing flows. Here, a theoretical mixing model has been developed from first principles and validated by the experimental measurements. For the first time, a method to quantify the mass fraction of the fluid carried over from upstream egress into downstream ingress has been presented and measured; it was shown that this fraction increased as the downstream sealing flow rate increased. The upstream purge was shown to not significantly disturb the fluid dynamics but only partially mixes with the annulus flow near the downstream seal, with the ingested fluid emanating from the boundary layer on the blade platform. From the analogy between heat and mass transfer, the measured mass-concentration flux is equivalent to an enthalpy flux, and this re-ingestion could significantly reduce the adverse effect of ingress in the downstream wheel-space. Radial traverses using a concentration probe in and around the rim seal clearances provide insight into the complex interaction between the egress, ingress and mainstream flows.

Evaluating the Effect of Vane Trailing Edge Flow on Turbine Rim Sealing

“…Scobie et al [18] studied ingress and egress in a 1.5-stage turbine test rig and quantified the egress flow from the upstream wheelspace cavity that is ingested into the downstream wheelspace cavity. In their study, the authors used effectiveness measurements and radial traverses upstream and downstream of the turbine blade to study the effects of cooling flow being "carried over" into the following wheelspace cavity by re-ingestion.…”

“…One full vane pitch of data was collected at 0.1 vane pitch increments, as well as a total of 22 points in the radial direction were collected. A higher number of points were collected near the inner diameter wall to better resolve the gradient of CO 2 egressed from the wheelspace cavity that migrates along the inner turbine wall as described by Scobie et al [18]. Each radial location data point in the two figures is an average of the ten pitch increment points that covered the full vane pitch in the circumferential direction.…”

Aerodynamics and Sealing Performance of the Downstream Hub Rim Seal in a High-Pressure Turbine Stage

“…They measured an asymmetric egress distribution in the annulus at the edge of the seal clearance, driven by the annulus pressure profile. Scobie et al [8] quantified the re-ingestion of the upstream hub cavity purge into the downstream one, using seed gas concentration measurements. They concluded that the upstream injection partially mixes with the annulus air stream close to the downstream seal, reducing the adverse effects of ingress.…”