Clean Sky 2 identifies the Very High Bypass Ratio (VHBR) geared turbofan engines amongst the main candidates to reduce aviation’s impact on environmental pollution for near-future large civil aircraft applications. Innovative technologies for VHBR geared turbofans are expected to improve fuel efficiency by more than 25% with a view towards achieving the ACARE Flightpath 2050 targets. Despite the potential benefits of the new VHBR geared engine architectures, specific challenges and limitations have been identified in terms of the performance at the edges of the operating envelope, such as idle and sub-idle operation.
The project PROTEUS (PeRformance & Operability of Turbofan Engines Under Sub-idle) focused on the research and development of tools and methods capable of predicting the idle and sub-idle performance and operability of VHBR geared turbofan engines. This was achieved through detailed component aerodynamic performance characterization of validated high-order methods, which were subsequently reduced to 0D, and integrated for rapid whole-engine analysis. Through a better understanding of the idle and sub-idle performance of the next generation of large turbofans, project PROTEUS directly contributes towards enabling the Topic Manager, Rolls-Royce plc, and the European aviation industry meet Flightpath 2050 targets. The work also enables sub-idle considerations to be included in the engine’s preliminary design process and aid in certification.
PROTEUS capitalises on several in-house methods, developed by the Consortium partners, for idle and sub-idle component performance analysis and representation. The Consortium comprised three Universities: Cranfield University (CU) in the UK (Consortium Lead), University of Cambridge (UCAM) in the UK and the Karlsruhe Institute of Technology (KIT) in Germany. (See Figure 1).
The overall objectives set to achieve the aim of this work are described as follows:
1.Improve understanding on axial-flow compressor operation under idle and sub-idle conditions and develop methods to predict sub-idle performance including the effects of bleed valves and variable geometry, heat soakage and stall drop-in during cranking and light-up.
2.Understand staged lean-burn combustor operability within a VHBR geared turbofan at sub-idle conditions and the effect of spray pattern and heat release on the combustor performance.
3.Understand the idle and sub-idle performance of the LP system by analysing fan-intake interactions, installation effects from the wing and aircraft on the exit pressure field, and turbine performance.
4.Integration of methods and tools for component characterisation in NPSS to calculate whole-engine performance at sub-idle and idle conditions.
