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Advanced Research Into Aeromechanical Solutions

Periodic Reporting for period 1 - ARIAS (Advanced Research Into Aeromechanical Solutions)

Reporting period: 2018-09-01 to 2020-02-29

The overall goal of the ARIAS project is to improve the design methods employed by aircraft engine manufacturers to predict aeromechanical vibrations which occur due to the interaction of the component vibration with the air flow through the machine. The current industry standard methods are limited in their ability to predict when aeromechanical vibrations will affect the structural behaviour of the machine. If unexpected and harmful vibrations are discovered during the testing phase, this will lead to a redesign, which will add significant cost and time to the overall product development process. In-practice, the limitations of current methods generally lead to over conservative designs, where unwanted aeromechanical behaviour is avoided at the expense of cost, weight and complexity in the components. In the most extreme cases, aeromechanical vibrations can compromise the structural integrity of engine components, which can have significant safety and reliability consequences. Having access to more reliable design methods will enable optimisation of aeromechanically acceptable component designs, facilitating the production of more efficient, reliable and quieter engines in line with the ambitions of ACARE2020 and Flightpath 2050.
The study of the aeromechanical vibrations is difficult due to the complex physical processes involved and the importance of the interaction between these processes. The objective of the ARIAS project is to improve the current understanding of the physical processes that cause the harmful vibrations in aircraft engines.
More specifically, the objectives of the project are:
• improve the design methods employed by aircraft engine manufacturers to predict aeromechanical behaviour
• expand the available database of experimental aeromechanical measurements
• develop validated analytical methods that can be used to support engine certification
• reduce product development time and costs
• advance the state of the art in the understanding of the underlying physics of aeromechanical vibrations
• investigate new and advanced technologies for the mitigation and monitoring of aeromechanical vibrations
• enable engine manufacturers to design more efficient (eco-friendly), quieter and more reliable engines
During the first phase of the project the main focus was on design of the experiments, including design and manufacturing of new components, instrumentation and detailed planning of the test campaigns. At the same time significant efforts have been put on the modelling side to support the design of the experiments as well as to enable the implementation of some of the innovative and advanced methodologies foreseen by the project objectives. The planned extensive experimental campaigns involve 7 different test rigs across the Europe, complementing each other to provide a unique set of test data which will enhance understanding of aeromechanical behaviour of the turbomachinery components (compressor –and turbine blades and labyrinth seals). The technical work is organized in four work packages:

WP1 Flutter and forced response in compressors
Focus for the first 18 months has been on planning the tests, designing the required new components and instrumentation, design supporting and pretest numerical predictions. Manufacturing of all the parts required for the aerodynamic forcing measurement campaign in transonic compressor rig at TU Darmstadt, has been completed. Design of the KTH cascade rig for aerodamping measurements at high reduced frequency has been finalized and manufacturing of the parts is ongoing. The electromagnetic blade excitation system enabling aerodynamic damping measurements in the U. Stuttgart closed loop compressor rig has been verified. An existing rotor blisk has been redesigned to hold a ring damper for the ECL vacuum rotating rig tests enabling measurement of mechanical damping and characterization of split ring dampers

WP2 Forced response-flutter interaction in turbines
An existing bladed-disk has been redesigned to fit the purpose of the project. A new disk with a different number of attachments has been and manufactured and the rotor blades re-worked to accommodate a second magnet. A set of dampers, fixing devices, magnet frames and other accessories have been procured. Simultaneously, a vacuum spinning rig has been redesigned to include a second stationary frame to support a second set of magnets and optical probes. The excitation of this second set of magnet will be superimposed with the primary one.

WP3 Flutter in labyrinth seals
Much of the work undertaken so far within WP3 has been the design of the entirely new labyrinth seal test rig. It started with requirements capture to ensure that the rig will deliver the desired experimental data while still meeting the cost and timescale constraints of the project. Concept and detailed design work followed, with technical reviews held at regular intervals to make key decisions, address technical challenges and approve designs. The final design has now been completed and includes a range of highly innovative features that allow us to explore a large seal design space at low cost and timescales. These include: reversible flow for rapid testing of non-symmetrical seals, acoustic tuning to instigate or inhibit interaction with the seal, variable seal clearance within a single test set-up and the ability to stimulate standing or travelling waves on the seal. In parallel with the rig design work, a datum seal test article has been designed and subjected to aeromechanical analysis using both current industry standard methods and updated seal flutter approaches developed as part of early work within ARIAS WP4. These have provided confirmation that the combined rig and datum test article will exhibit the aeromechanical instabilities that we wish to measure and study closely. WP3 has now moved into the hardware procurement, rig build and commissioning phase prior to initial testing planned for later this year.

WP4 Future enabling technologies
Initial effort has been dedicated in supporting the redesign of the AvioAero spin rig in order to allow the superimposition of flutter and forced response to be replicated in the vacuum chamber, and after that preliminary activity has started to develop innovative methodology to assess that overlap. Moreover, a novel methodology has been developed to better predict 1D flutter stability of labyrinth seal and it has already been used to support WP3 seal flutter rig design. Finally, preliminary numerical activity in developing a new methodology to determine flutter vibration from acoustic emission has been tested on previous experimental data available and innovative tip-timing post processing has been implemented In order to deal with both synchronous and asynchronous vibration monitoring at the same time.
The experimental data and methods developed within the ARIAS project will have direct application in both understanding and interpreting the behaviour and measurement data produced by the demonstrator and development engines and optimising the design of the subsequent production families of engines. It will create an accelerated impact on vibration related redesigns of current turbofan engines and the design of new more efficient, reliable and robust engines.The generated knowledge will also improve the quality of the education of future engineers in turbomachinery aeromechanics.