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Full Aero-thermal Combustor-Turbine interactiOn Research

Final Report Summary - FACTOR (Full Aero-thermal Combustor-Turbine interactiOn Research)

Executive Summary:
To reduce fuel consumption and CO2 / NOx emissions, modern turbo-machineries operate at high velocities and high temperature conditions. The lack of confidence in the prediction of combustor-turbine interaction leads to apply extra safety margins on components design.
Consequently, the understanding of combustor-turbine flow field interactions is mandatory to preserve high-pressure turbine (HPT) life and performance when optimising the design of new HPT and combustors (e.g. lean burn combustors).
The main objective of the FACTOR project is to optimise the combustor-HPT interaction design. This will be achieved through a better understanding of the interaction between the coolant system, the transport and mixing mechanisms enabling a Specific Fuel Consumption (SFC) reduction of about 2%.
To achieve this purpose a new turbine has been designed. This turbine has the same characteristic as a current engine turbine. This turbine has been designed by the most important European aeronautical actors and has been manufactured to be setup on the DLR rig. To be representative of an engine environment, a combustor simulator has been designed in order to produce a flow which has the same characteristic and the same hot point that may be found in real engine.
This turbine has been specially designed to allow high precision measurements which are not available in a real engine measurement but which are mandatory to have a better understand of the fluid structure and behaviour.
Optical access have been designed to allow non-intrusive measurements in the turbine, optical measurements have enabled to measure heat-transfer coefficient on both stator and rotor blades which are not measurable inside a real engine because of accessibility.
Once the test database has been available, new CFD calculations have been performed to see if the calculations are enough representative to reproduce the behaviour seen during tests. The objective was to find a suitable configuration and calculation parameters that may be used during future design to better predict the hot-point migration.

All these measurements have been concatenated to create a new test database which is available for all the FACTOR partners and will be used for the future design of turbine. This database is very complete because it contains different clocking positions that enable to better understand how the hot point interacts with the turbine. It also contains detailed measurements in all interfaces which will be available and used for at least 10years to better understand the fluid structure inside the turbine. It will also be used to be more predictive in future design to achieve higher efficiency engines.

Project Context and Objectives:
To reduce fuel consumption and CO2 / NOx emissions, modern turbo-machineries operate at high velocities and high temperature conditions. The lack of confidence in the prediction of combustor-turbine interaction leads to apply extra safety margins on components design.
Consequently, the understanding of combustor-turbine flow field interactions is mandatory to preserve high-pressure turbine (HPT) life and performance when optimising the design of new HPT and combustors (e.g. lean burn combustors).
Previous projects have investigated combustor technologies to improve combustor volume, cooling, emissions and exit temperature profiles (INTELLECT and TIMECOP) and others addressed the challenge of understanding the behaviour of hot flow structures in the HPT (TATEF2 and AITEB2). All those projects gave a better understanding of the physical behaviour of the combustor and the turbine and brought improvements on the designs of both modules.
However industrial experience demonstrates that the separate optimisation of the two modules - combustor and turbine - does not necessarily ensure that the system in which they are embedded will also be optimum. This understanding is even more crucial to develop new combustion technologies (e.g. lean burn combustion) where there is a lack of industrial experience.
The link between the combustor and the turbine in an engine is very tight and all engine manufacturers are putting a strong effort to master this interface: extremely hot gases, variable boundary layers, turbulence effects and inherent unsteadiness are some of the phenomena making this region of the engine a difficult interface. This interface still requires strong improvements as gas turbine designers are lacking the experimental data needed to optimise its design.
The main objective of the FACTOR project is to optimise the combustor-HPT interaction design. This will be achieved through a better understanding of the interaction between the coolant system, the transport and mixing mechanisms enabling a Specific Fuel Consumption (SFC) reduction of about 2%.
To get a detailed understanding of the combustor-HPT interactions, FACTOR will set up an experimental test infrastructure using most advanced measurement techniques. These measurement techniques will be adapted to FACTOR specific requirements and all combined to ensure that an all-encompassing and comprehensive database of measurements is obtained together, respecting exactly the same boundary conditions. This unique test infrastructure involves two complementary European turbine test rigs:
• A new continuous flow facility hosted by DLR (Deutsches Zentrum für Luft- und Raumfahrt). Fed by hot and cold air, this module will supply realistic flow field to the downstream HPT and thus enable experimentalists to explore the aerodynamic and thermal interactions between combustor and turbine.
• A complementary blow-down turbine facility hosted by Oxford University (the Oxford Turbine Research Facility O-TRF) that will be used to supplement the analysis of the DLR continuous flow test rig.


The turbine modules which have been plugged on the DLR rig have been designed and manufactured during the first part of the project.

Before starting any detailed design, the first objective of the project was to choose main parameters of the future with three requirements:
• The rig has to be representative of current engine technology
• The rig must be compatible with most advanced measurements technics
• The tests have to be reproducible
• The comparison with calculation has to be easiest as possible
These three requirements have been declined in design objectives for all parts of the turbine:
• Well-chosen periodicity of each part of the turbine enables to perform representative high-fidelity CFD without computing the entire turbine. The objective was to design a turbine with a 2Pi/20 periodicity which enables to make high accuracy CFD at a reasonable cost.
• The operating point of the turbine will be a high subsonic one which is representative of current high-pressure turbine.
• The combustor simulator must be “clockable” to change the position of the hot point relatively to the NGV grid.
This enables to investigate two different configurations. A leading edge configuration, in which the hot point will hit the leading edge of the NGV grid. A passage configuration, in which the hot point will be targeted between two NGV to prevent it from blowing up and see how it interacts with the rotor.
To achieve this purpose a one-stage and half HP turbine has been designed. The challenge of this kind of project is to design a facility which is representative of a real engine module but in which high precision measurements can be easily performed. That’s why the temperature has been lowered to a level that makes intrusive measurements possible (around 500K-700K). Even-if the temperature is much lower than in an engine, the aerodynamic behaviour of the turbine is representative of the most recent engines. The design of the FACTOR required also to design a combustor simulator which produces an exit flow which is representative of a real engine in term fluid structure and temperature gradient. The objective is to be representative of a real combustor without burning any fuel.
So the temperature is raised by an electrical device which enables to easily control the temperature level at the exit of the combustor simulator.

The turbine was not the only part which had to be designed in the project, as matter of fact suitable instrumentation devices had to be designed to be compatible with the rig:
• Traverse measurements in each plane. This measurement enables to have a detailed mapping of the flow in a given plane
• Optical access to the rig :
o Performing RAMAN measurements
o Performing heat-transfer measurements

The combustor simulator was the first part of the rig which has been designed in detailed. As this part is very import to have a turbine which is representative of a real engine, the decision has been made to setup a facility at the University of Florence (UNIFI). This facility enables to measure the flow produced by the combustor simulator. As the measurements have been available during the module design, the measurement results have been used to control that the HP module will correctly respond to the inlet flow.
To simplify the experiment, only three sectors have been mounted on the rig. Later it was also decided to add Nozzle Guide Vane after the combustor simulator to measure how the hot point will go through the NGV stage. This rig was also useful to perform measurement formerly scheduled on the DLR rig which have been removed from the test campaign in order to save time.

The design of the turbine was also made to allow operating at different points:
• Design operating point : high subsonic point
o Both passage and Leading edge clocking
• Isothermal conditions
• Uncooled conditions
• Off-design operating point : supersonic point

The test campaign aims at obtaining producing results which will be used for comparison with calculations. For this purpose, the measurements should satisfy these requirements:
• Enough detailed results to allow an easy comparison the continuous CFD
• Under-control uncertainty to be confident in the comparison
• The results of the campaign will give strong information about:
o The inlet condition at the inflow of the NGV
o Detailed results in all the interface planes
• Good control of the turbine parameters
o Main stream massflow
o Accurate measurement of the cooling massflow
o Accurate measurement of secondary massflow (cavity for example)

By satisfying all these requirements, the FACTOR rig will allow to setup a strong experimental database which will be used for detail comparison with CFD.
Once the experimental results are available, the second objective of the project is to compare the design calculations to see if the predicted behaviour of the turbine is similar to the one observed during tests.
Then, the final objective is to perform CFD with different configuration to find the better way to predict the migration of the hot point through the turbine. At this stage, the CFD won’t be performed on preliminary operating point with theoretical boundary conditions, but some results of the rig will be used to update CFD boundary conditions.
So, the main objectives of the project may be summarized this way:
• See how the hot point migrate through the turbine on a well-controlled environment.
• Find a good calculation setup which enables to reproduce the behaviour seen on the rig.
• Apply this calculation setup on future engine design to optimize the engine consumption.

Project Results:
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Potential Impact:
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List of Websites:
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