Session: 38-05 Gas Turbine Engine Transition Ducts and Flow Interactions II

Paper Number: 82458

82458 - The Interaction of Main Stream Flow and Cavity Flows in Turbine Center Frames and Turbine Vane Frames 

In modern turbofan engines, all turbine stator-rotor cavities are purged with cold air, drawn off the compressor stages, to prevent hot gas ingestion in the cavities from the main flow. The purge air ultimately leaves the cavities and is convected downstream through the annulus, where it mixes with the main stream air and interacts with the secondary flows, developing through the turbine vane and blade rows.

This paper focuses on the interaction between the last High-Pressure Turbine (HPT) stage purge flows and the Inter-Turbine Duct (ITD), the S-shaped channel guiding the flow from the HPT to the first Low-Pressure Turbine (LPT) stage. Two state-of-the-art ITD configurations are analyzed in this work: the Turbine Center Frame (TCF), which is supported by symmetric aerodynamic strut fairings and generally adopted in conventional dual-spool engines; and the Turbine Vane Frame (TVF), which features turning struts and splitters and is typical of geared turbofan engines.

The measurement campaigns for both setups were carried out in the Transonic Test Turbine Facility of Graz University of Technology (Institute of Thermal Turbomachinery and Machine Dynamics). The test vehicles consist of an HPT stage, the ITD (TCF or TVF) and the first LPT vane or blade row. The same HPT stage was used for both duct solutions, to enable consistent, engine-representative inlet conditions between the two setups. All hub-shroud, upstream-downstream HPT stator-rotor cavities are supplied with purge flows by a secondary air system, with independent mass flow and temperature control for each purge line.

Five-hole probe data were acquired at the inlet and outlet sections of the ITDs, to characterize the aerodynamic flow field entering and leaving the duct. In addition to the pneumatic probes tests, seed-gas concentration measurements were performed in the same planes, to track down the seeded cavity air in the main stream and investigate its post-egress behavior. Finally, detailed post-test CFD results are presented to obtain additional insight into the flow phenomena developing through the strut passage.

The concentration effectiveness field at the inlet of the ducts shows the same characteristics in both configurations: the upstream purge flows are entrained in the HPT rotor secondary flows, leading to high-concentration spots that influence large portions of the channel. On the other side, the downstream purge air is confined into a thin concentration boundary layer in close proximity to the endwalls. The thickness of this boundary layer is affected by the circumferential pressure distribution from the HPT vanes and struts. At the TCF and TVF outlet, the upstream purge forms a circumferentially un-interrupted band, shaped by the secondary vortices evolving through the duct. The downstream purge interaction with these vortices leads instead to the formation of well-bounded lobes, whose size, count, and position are inherently related to the nature of the duct vortices and thus differ significantly between the two cases.

Presenting Author: Filippo Merli Graz University of Technology

Presenting Author Biography: Filippo Merli was born in Piacenza (Italy) in 1993. He earned his bachelor’s degree in Mechanical Engineering in 2015 and then his master’s degree in Energy Engineering in 2018 at Politecnico di Milano. The same year he moved to Graz, where he is currently pursuing his Ph.D. degree at the Institute of Thermal Turbomachinery and Machine Dynamics of Graz University of Technology.

Authors:

Filippo Merli Graz University of Technology
Asim Hafizovic Graz University of Technology
Nicolas Krajnc Graz University of Technology
Malte Schien Graz University of Technology
Andreas Peters GE Aviation
Franz Heitmeir Graz University of Technology
Emil Goettlich Graz University of Technology