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Experimental Aero- and Thermal investigation for a next generation Engine Exit Module

Periodic Reporting for period 1 - EATEEM (Experimental Aero- and Thermal investigation for a next generation Engine Exit Module)

Reporting period: 2018-10-01 to 2020-03-31

Beyond 2020, new efforts are required to improve the engine efficiency and fuel burn to meet the Advisory Council for Aeronautics Research in Europe (ACARE) goals for the year 2035 and 2050. The year 2050 targets aim for a 75% reduction in CO2 emissions, a 90% reduction in NOx emissions, and a 65% reduction of the perceived noise relative to engine and aircraft performance of the year 2000. It is commonly agreed that the geared turbofan engines have the potential to make a significant step towards the above targets. The Advanced Geared Engine Configuration and the Very High Bypass Ratio Turbofan are two crucial radical engine architectures selected to be matured within the ENGINES ITD of the Clean Sky 2 Programme.

To further increase the engine efficiency and reach CO2 emission targets, the expansion system is constantly challenged by reducing gas path pressure losses, widening the operational envelope, and allowing for ever-increasing geometrical complexity of structural components. For the Turbine Rear Structure (TRS) and the Engine Exit Module (EEM), the new engine architecture imply that designs are needed that can withstand higher temperatures and temperature variations, operate under more severe LPT off-design conditions, present lower pressure losses, and be lighter and still provide performance benefits.

Chalmers and GKN Aerospace Engine Systems are collaborating in this Clean Sky 2 project, won by Chalmers in the open call for partners, with GKN as the Topic Manager. A unique facility for experimental testing of engine exit modules (EEM) at engine-realistic flow conditions is currently available at Chalmers' Laboratory of Thermal and Fluids Science and is used for testing of novel EEMs for future efficient aero-engines. The unique design of the facility includes an open test section that permits investigation of the complete EEM assemblies consisting of a turbine rear structure (TRS) and a core exhaust nozzle. The facility is equipped with a 1.5 stage shrouded low-pressure turbine (LPT) providing realistic inflow to the tested EEM.

The overall concept of EATEEM is to mature expansion system technologies so that they become key enablers for reducing CO2 emissions and engine mass for the Advanced Geared Engine and Very High Bypass Ratio Turbofan configurations in the ITD work package of Clean Sky 2 Programme. Thus, EATEEM is a part of the work package defined to bring the expansion technologies to TRL 4. The EATEEM project test infrastructure will enable further research on EEM improvement and allows for the investigation of state-of-the-art EEM concepts to be used in the next generation of aero engines.
Project efforts will demonstrate the feasibility and benefits of novel aerodynamic concepts of the engine exit module (EEM). The following objectives have been achieved from the beginning of the project:

Objective 1. Proof-of-concept and laboratory validation of four novel EEM architectures. A test section of one of the novel EEM architecture was designed, manufactured, assembled, and fully instrumented. The tests will be performed in a unique facility at a representative upstream LPT stage, inlet conditions and flow Reynolds numbers for the demonstration up TRL 4 as specified in the targets.

Objective 2. Characterization of the aerodynamic performance of novel EEM architectures. Currently, Build 1 test-section is fully instrumented. State-of-the-art instrumentation was performed and validated for goals specified in the targets: accuracy better than 0.1% for total pressure differences, better than 1.5 Pa for multihole probe and wall pressures and better than 1% for the axial velocity; instrumentation for the investigation of the laminar-turbulent transition and flow separation margins and their effect on the aerodynamic performance of the novel EEM designs; the instrumentation for the investigation of the flow separation by a nonintrusive Particle Image Velocimetry (PIV) method for the best possible accuracy of the results; the investigation of the effect of the flow Reynolds number, tip leakage, inlet swirl angle, purge flow and real geometry effects.

Objective 3. Investigation of the heat transfer for the Build 1 novel EEM architecture. Instrumentation for heat transfer studies has been performed and the heat transfer measurement methods were developed in detail. Currently, Build 1 test-section is fully instrumented to provide this data and the measurement methods are validated as specified in the targets: to assess the heat transfer characteristics of the EEM Build 1 with very high measurement accuracy, better than 0.2K for temperatures and temperature differences, resulting in the accuracy of the heat transfer coefficient better than 5% on at least 50% of the surfaces; the method was validated for study of the influence on the heat transfer of the laminar-turbulent transition location and flow separation; the method is validated to study the influence on the heat transfer of the flow Reynolds number, tip leakage, inlet swirl angle, purge flow and real geometry effects.

Objective 4. Provided input data and hardware for exploring new EEM functionalities and EEM optimization. Experimental data, hardware, and professional experience from the EATEEM project is already a valuable input. Within the frame of the project the synergy is established between the EATEEM and other aircraft/aero-engine research projects: a national-program research project where the primary focus is on the influence of manufacturing non-conformances on TRS performance; a European research project ENABLEH2 which is focused among other topics on core exhaust heat rejection in TRS.
CHALMERS’ TRS/EEM facility offers several unique opportunities compared to other rigs. The construction of the test section of CHALMERS’ TRS/EEM facility allows for testing the entire EEM assemblies and allows arbitrary shapes of the EEM test sections including polygonal walls. The facility is low-speed high-Reynolds number type which means continuous operation and long experimental runs for highly detailed and accurate measurements. The facility has very high flow stability and repeatability of the setpoint parameters. To our knowledge, the EATEEM project is the first experimental EEM validation project providing a complex aero-thermal analysis of TRS modules by several accurate measurement techniques, which makes the EATEEM outcome unique in its value and data reliability. The EATEEM project will give an exceptional opportunity to push the measurement accuracies for all used measurement techniques to their upper limits by minimizing the measurement uncertainties based on our experience from previous research projects. The EATEEM will provide experimental validation data for several new concepts. The EATEEM data will be used for validation of new improved optimization and numerical prediction methods for aerodynamic and heat-transfer performance. Furthermore, the experimental methods and hardware from the EATEEM will be used in future research projects devoted to the development of the EEM. Within the frame of the project, the synergy is established between the EATEEM and other aircraft/aero-engine research projects. A national-program research project where the primary focus is on the influence of manufacturing non-conformances on TRS performance. A European research project ENABLEH2 is focused among other topics on core exhaust heat rejection in TRS.
Chalmers University dedicated TRS/EEM experimental facility, with Reynolds range capability