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

Paper Number: 82502

82502 - Aerodynamic Assessment of Turbine Center Frames and Turbine Vane Frames Under the Influence of Purge Flows 

This paper investigates and compares the aerodynamics of two state-of-the-art configurations for the Inter-Turbine Duct (ITD) in a turbofan aero-engine: the Turbine Center Frame (TCF), which is typical of conventional dual-spool engines and features symmetric aerodynamic strut fairings, and the Turbine Vane Frame (TVF), which integrates a set of turning struts and splitters directly in the duct, thus enabling length and weight benefits at engine system level.

The measurement data utilized for the analysis are a product of almost ten years of research at Graz University of Technology, involving multiple test campaigns with either TCF or TVF setups at consistent inlet conditions. The experimental tests are carried out in the Transonic Test Turbine Facility at the Institute of Thermal Turbomachinery and Machine Dynamics (Graz University of Technology). All test vehicles include not only the ITD (TCF or TVF), but also the last High-Pressure Turbine (HPT) stage and the first Low-Pressure Turbine (LPT) vane or blade row, in order to ensure engine-representative conditions at the duct inlet and outlet sections. For the same purpose, the test facility supplies all the stator-rotor cavities with purge air, with independent control of temperature and mass flows for each cavity.

The measurements are performed with pneumatic probes (five-hole probes, Kiel-head rakes) at the inlet and outlet of the ITDs, for three different HPT purge flow rates, and corroborated with detailed CFD results. The aerodynamic comparison between TCF and TVF setups is discussed based on four key topics: duct inlet flow field, duct outlet flow field, duct total pressure losses, and duct aerodynamic excitation on the LPT rotor blades. For each one of them, the sensitivity to HPT purge variation in both configurations is evaluated.

Due to the presence of turning struts and splitters inside the ITD, the TVF shows a more complex outlet flow field than the TCF, characterized largely by the interaction of HPT purge flows and TVF secondary phenomena. The TVF total pressure loss was found to be less sensitive to purge variation compared to an advanced TCF design with high casing slope. These two mechanisms need to be considered in the aerodynamic design of TVFs. While the weaker TVF loss derivative to HPT purge may provide off-design operating point benefits relative to a TCF-based engine, the increased level of flow non-uniformity at the TVF exit, distributed over a wider range of engine orders, represents a design challenge for the first-stage LPT rotor.

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