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Composite AeroelasTics ANd Aeroacoustics

Periodic Reporting for period 1 - CATANA (Composite AeroelasTics ANd Aeroacoustics)

Reporting period: 2019-09-01 to 2021-02-28

Aircraft engines of the future must be efficient during flexible operation while emitting minimal pollutant gases and noise. A key factor to achieve these goals is to build larger turbojet engines to maximize the bypass flow while reducing the core size.
In the last decade a step changing progress has been enabled with the availability of lightweight gearboxes, capable to transmit the power from the low-pressure turbine to the fan. This allows to increase the diameter of the fan and to optimize it independently from the required rotation speed of the turbine, enabling higher bypass mass flow at reduced pressure ratio and relative speeds which is beneficial for compression efficiency and noise generation. To avoid additional weight induced by larger fan blades, high-performant composite materials are necessary to fully exploit this potential.
Long established design criteria which result partly from semi-empirical studies are not transferable to this novel technology, particularly concerning fluid-structural interaction mechanisms.
This project aims to promote the development of the next generation of UHBR Turbofan engines by closing the knowledge gaps concerning multi-physical interactions which affect performance and limit the stability range.
The overall objective of the project CATANA is:
- to analyse and interpret highly-coupled fluid-mechanical instability mechanisms from a representative composite fan to enable more accurate prediction methods.
- to achieve this goal an open-test-case-composite stage has been designed, which will be used for detailed structural analysis and to perform exhaustive steady and transient investigations with synchronized multi-physical instrumentation at all critical limits of the operating range.
Therefore, the following main objectives have been defined:
1. Establish advanced experimental methodologies based on synchronized instrumentations to investigate multi-physical interaction processes in the highly-coupled system.
2. Provide an exhaustive experimental database to characterize instability mechanisms physically and phenomenologically depending on operating conditions.
3. Derive the sensitivity of performance and stability towards structural system symmetry.
4. Analyse the influence of the intake geometry on system stability.
The most significant result of the work done within this project so far, is the development of the final fan (and stage) geometry on the basis of state-of-the-art research standards and its validation by industrial procedures. The design chain, based on an in-house parametric blade generator and the commercial CFD-solver FineTurbo, coupled with a structure-dynamic composite layer analysis in Ansys was used to derive a rotor blade geometry, that fulfils the requirements of a fan representative for near future low-speed fans. The final design was validated at a Critical Design Review with Safran Aircraft Engines in January 2020. Same applies to the OGV and other accessory parts of the machine. For all parts fabrication documents have been finalized and the parts have been ordered with different manufacturers in spring 2020. All metallic parts (OGV, Nose-Cone, Rotor platforms) have already been fabricated and controlled. Furthermore, the moulds for the rotor blades have been manufactured, first prototypes have been finished, and reception of all controlled blades is expected in 7/2021.
In order to introduce the designed rotor as an Open-Test-Case, the geometry has been presented at the ETC conference 2021 in publications UHBR OPEN-TEST-CASE FAN ECL5/CATANA Part 1 and Part 2. Additionally, open-access data formats for the dissemination of the test case have been determined and will allow a rapid and purposeful dissemination. The CATANA website has been created and will provide information to gain access to the test case geometry.

To enable an appropriate design of experiments time-linearized calculations have been successfully carried out with the result, that at the relevant speedlines the occurrence of flutter can be excluded between choke and maximum pressure operation, as published in 4/2021 at ETC conference. Additionally, unsteady near stall simulations have been performed and indicate safe operation at relevant speeds. Moreover, a method to model Non-Synchronous Vibration [Stapelfeldt, S. & Brandstetter, C. (2020): Non-synchronous vibration in axial compressors: Lock-in mechanism and semi-analytical model. Journal of Sound and Vibration, Volume 488, doi:10.1016/j.jsv.2020.115649; Brandstetter, C. & Stapelfeldt, S. (2021): Analysis of a linear model for Non-Synchronous Vibrations near stall, European Turbomachinery Conference 2021, Paper 592] and incorporate mistuning [Stapelfeldt, S. & Brandstetter, C. (2021): Suppression of non-synchronous-vibration through intentional aerodynamic and structural mistuning, accepted for ASME 2021 and Journal of Turbomachinery] has been developed and will soon be published at the ASME conference. This model will be used to find an optimal mistuning pattern of the manufactured blades based on the structure analysis.
Furthermore, ECL already started to perform preparations of the facility, particularly concerning instrumentation. A system to manufacture the abradable liner was developed and fabricated to ensure concentric tip clearance. Also, modifications on the control systems were conducted to enable transient measurements with automatically controlled shaft speed and throttle degree mechanisms. Acquisition capabilities were increased for the surveillance of blade and machine vibrations and a tip-timing system for the surveillance of rotor blade vibrations has been ordered at MTU aero engines. Accessory parts for PIV measurements were designed and fabricated and wall pressure sensors have been ordered and received as well.
The whole concept of Project CATANA is dedicated to the philosophy laid out in the H2020 Open Access Pilot. The manifold of research opportunities arising from the CATANA outcomes can be a key enabler for more collaborative and purposeful actions within the European research community.
The availability of a composite-fan representative open-test-case is of undisputed value for the European Research community for interdisciplinary method development and validation. The proposed fan stage is not only an improvement of existing test cases but will be the first one available at all, which will be openly shared including geometry, structural properties and multi-physical steady and transient measurement data.
Through achievement of the described research objectives, the scientific impact to the European research community of the results will encompass diversified disciplines. Understanding and quantification of instability mechanisms will support the development of multi-physical prediction models.

Project CATANA will therefore contribute to the closing of the prevailing knowledge gaps on multi-physical interactions, and thus enable a consequent implementation of UHBR concepts. As a result, significant cabin and community noise reductions can be achieved through the lower rotation speed of the fan compared to state-of-the-art engines. Furthermore, the emission of the greenhouse gases CO2 and NOx can be significantly reduced, which leads to a lower impact on climate change.
Installation of fan EC5/CATANA in machine core
Front view of fan ECL5/CATANA
Overview of test cell PHARE-2 / ECL-B3