Analysis of Heavy Duty Gas Turbine Stator-Rotor Cavity Through 3D CFD-1D Fluid Network — Field Measurements Combined Approach

Abstract

An effective design and development of the Secondary Air System of a heavy-duty gas turbine is crucial for many purposes, such as cooling and sealing air supply, pre-swirling features, leakages control, casings and rotor thermal state assessment and rotor axial thrust management. All of these features directly impact on the performances and integrity of the whole machine and accordingly require advanced design approaches. The first stage stator-rotor turbine cavity of Ansaldo E-Class heavy-duty gas turbine AE94.2 underwent design modifications to adjust its internal pressure and consequently lower the global rotor axial load acting on the thrust bearing. This goal had to be reached while maintaining safety against hot gas ingestion from the turbine section main flow into the cavity, thus preserving the GT integrity. A multi-purpose analysis was then carried out on the cavity Secondary Air System. This involved steady 3D CFD calculations with a computational domain comprising the first turbine stage and the corresponding stator-rotor wheelspace. A combined use of CFD and SASAC, the in-house Ansaldo 1D fluid network code, finally led to an upgraded design of the cavity. Two field measurement campaigns were subsequently carried out on an AE94.2 GT to validate both the baseline configuration and the upgraded one, by means of 6 pressure and temperature sensors in the cavity and 12 load cells/thermocouples on the thrust bearing. The CFD model and results are presented, the fluid network tuning is discussed and the experimental setup and main outcomes of the two field campaigns are reported. Constant references to the definitive literature are made, with an effort to correlate at best research and industrial practice. These integrated activities allowed to perform a reliable verification against hot gas ingestion into the stator-rotor cavity and to successfully develop an effective solution, which reduced the GT rotor residual axial thrust by up to 25% less.