Influence of Leakage Flows on Hot Gas Ingress

Abstract

One of the most important problems facing gas turbine designers today is the ingestion of hot mainstream gases into the wheel-space between the turbine disk (rotor) and its adjacent casing (stator). A rim seal is fitted at the periphery and a superposed sealant flow—typically fed through the bore of the stator—is used to prevent ingress. The majority of research studies investigating ingress do so in the absence of any leakage paths that exist throughout the engine's architecture. These inevitable pathways are found between the mating interfaces of adjacent pieces of hardware. In an environment where the turbine is subjected to aggressive thermal and centrifugal loading, these interface gaps can be difficult to predict and the resulting leakage flows which pass through them even harder to account for. This paper describes experimental results from a research facility which experimentally models hot gas ingestion into the wheel-space of an axial turbine stage. The facility was specifically designed to incorporate leakage flows through the stator disk; leakage flows were introduced axially through the stator shroud or directly underneath the vane carrier ring. Measurements of CO2 gas concentration, static pressure, and total pressure were used to examine the wheel-space flow structure with and without ingress from the mainstream gas-path. Data are presented for a simple axial-clearance rim-seal. The results support two distinct flow-structures, which are shown to be dependent on the mass-flow ratio of bore and leakage flows. Once the leakage flow was increased above a certain threshold, the flow structure is shown to transition from a classical Batchelor-type rotor-stator system to a vortex-dominated structure. The existence of a toroidal vortex immediately inboard of the outer rim-seal is shown to encourage ingestion.

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

“…The authors also found an inflection in the rim sealing effectiveness behavior at the rim seal location in both engine spans. This inflection has also been reported by other authors in previous studies [14][15][16][17].…”

An Improved Control Method of Rim Seal Based on Auxiliary Sealing Holes

“…In the past two years, turbine designers has realized that this leakage flow (CHL) has the potential to improve the sealing efficiency of rim seal. Both Clarks (Clarks 2018) and Patinios (Patinios 2018) found that when the sealing air flow rate is constant, the excessive CHL flow will cause the "toroidal vortex" in disk cavity, which has negative effect on sealing efficiency. But under certain CHL flow rate, the Batchelor flow pattern inside the cavity can be maintained, and the sealing efficiency can be improved.…”