Hot gas ingestion in gas turbines
Ingress is one of the most important of the cooling-air problems, with considerable international research effort devoted to finding acceptable design criteria.
Turbine rotor disks are among the most highly stressed components in the engine. Metal temperatures must be limited to ensure acceptable life, integrity, and reliability. Rim seals are fitted at the periphery of the wheel-space between the turbine disk and its adjacent stator. This reduces the ingress of hot mainstream gases.
The ingress is caused by circumferential pressure asymmetries in the mainstream annulus, radially outward of the rim seal. A superposed sealing (purge) flow, bled from the compressor, is used to cool the rotor disk and to prevent, or at least dilute the ingress to a tolerable level. Superfluous use of this purge air can reduce the cycle efficiency. It's important to understand the fluid dynamics governing rim-seal performance.
We've designed two axial turbine test facilities to investigate hot gas ingestion:
- a single-stage facility (2008): built to investigates ingress into the wheel space of a single-stage rotor-stator system
- a 1.5 stage facility (2013): built to investigate ingress into the wheel spaces upstream and downstream of a rotor disc
Both test facilities are fluid dynamically scaled and operate at incompressible flow conditions. They are far removed from the harsh environment of the engine, which is not conducive to experimental measurements. The rigs feature interchangeable rim-seal components. This allows for flexible and effective data collection over a wide range of sealing-flow rates. The facilities efficiently rank and quantify the performance of generic and engine-specific seal geometries.
Our Centre has investigated the effects of ingestion experimentally, theoretically and computationally for almost a decade. We have published over 30 conference and journal papers on the topic.