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CROR Engine Debris Impact SHielding. Design, manufacturing, simulation and Impact test preparation

Periodic Reporting for period 3 - REDISH (CROR Engine Debris Impact SHielding. Design, manufacturing, simulation and Impact test preparation)

Reporting period: 2018-07-01 to 2019-03-31

New, eco-efficient aircrafts are challenged by a demand to significantly reduce the CO2 and NOx emissions. To achieve these goals, new configurations are being explored to integrate advanced engines and propulsion concepts in the aircraft. Most of such promising concepts (such as the CROR-engine (see Figure 1), Boundary Ingestion Layer (BIL), Ultra High Bypass Ratio engines (UHBR), multiple fans) cannot be targeted simply by replacing the engines of the current generation, but require a substantial change in the aircraft configuration.

Results from recent research programmes have provided much evidence that many of these concepts do lead to better gains of ecologic and economic efficiency by installing them on the rear end of the fuselage. This is motivated by the favourable spatial integration conditions in particular for large fan or rotor diameters or multiple fans, which can be the key for achieving unprecedented fuel efficiencies. In case of un-ducted engine architecture as the CROR, the rearward shift of the engines away from the wing provides additional advantages in cabin noise and passenger comfort and safety improvement. Regarding the safety, the main issue is the CROR engine debris that can be release with high energy when there is a failure. Therefore, it is mandatory to develop innovative solutions for panels and shielding able to shield and reduce damage at impact.

The goal of REDISH project is the development, maturation and down-selection of an innovative shielding solution able to sustain impacts from CROR engine burst debris while complying with aeronautical structural requirements and standards, namely regarding weight efficiency (the main source for fuel efficiency and reduction of emissions). A coupled experimental-simulation development approach at two structural scales (panel/laminate and component/structural) is proposed that starts from a large pool of possible configurations that will be down-selected in successive analysis steps of increasing event fidelity and structural detail until the best solution is reached. Virtual testing by means of high-fidelity simulation tools developed by the consortium will be used to decrease the need for costly physical testing as much as possible and accelerate the shielding development process.
REDISH is following a systematic down-selection strategy based on a high-fidelity numerical approach validated by experimental testing. The workflow of this innovative methodology is represented in Figure 2. An initial pool of shielding solutions identified as promising and that meet the design requirements defined by the TM is down-selected in stepwise processes that systematically evaluate the solutions at two major structural levels of increasing complexity: laminate level and structural/component level.

In the first step of the down-selection process (laminate level), materials screening for impact performance was carried by ranking the initial pool of promising solutions according to ‘performance’, ‘evaluation easiness’ and ‘implementation easiness’ weighted indicators, wherein the first one was evaluated by means of analytical/empirical formulations available in the literature. This resulted in the identification of more than 30 solutions, and derivations thereof, for the next evaluation step which already relied on high-fidelity finite element analyses. For these, the necessary material constitutive models were either developed in-house or were available in the finite element software package Abaqus/Explicit, selected in agreement with the Topic Manager (TM) to be used in the project. This performance evaluation resulted in a higher-fidelity ranking of more than 20 evaluated solutions and a second down-selection step to 14 solutions that were actually manufactured, and are being experimentally evaluated in the framework of another Clean Sky 2 project (ELEMENT, grant agreement nr. 715873). The experimental results at this level were used to yet another performance ranking on the 14 tested solutions, and to validate and improve the numerical models. The third down-selection step, based on experimental results, resulted in the identification of 5 families of impact shielding configurations that are being evaluated at component/structural level stage (Level 2).

The numerical analyses at Level 2 are being performed by means of a Computational Mechanics approach wherein mostly shell finite elements are used and the Continuum Damage Models, being intrinsically demanding in terms of the required computational resources, will be implemented in a ‘lean’ form, such that computational mechanics simulation at component/structure level is efficiently carried out. In particular, the modelling of the essential phenomenology associated with the behaviour of composites under impact and crushing loads is ensured. The modelling of the failure modes not associated with these load types is simplified if and when this will lead to a relevant reduction in the required computational resources. The high-fidelity numerical evaluation of the performance of the solutions will guide the process of manufacturing and experimental testing of structural panels in Level 2. This will lead to the final selection step in which the final solution to be applied on CROR engine debris impact shielding will be selected. The experimental results will also be used to validate the numerical simulations at component level.
There are three major waves of impact resulting from REDISH:
- The successful development impact shielding against high-energy engine debris is a condition for the implementation of CROR propulsion technology in the rear fuselage of future civil Regional Aircraft. The advantage of the CROR installation on the rear fuselage is motivated by the favourable spatial integration conditions, in particular for large fan or rotor diameters or multiple fans, which can be the key for achieving unprecedented fuel efficiencies and reductions in the CO2 and NOX emissions.
- High-energy composite impact shielding solutions will be developed that also cope with the lightweight requirements of aeronautical structures. This is an innovative pursuit that has only limited resemblance with military applications where weight- and cost-efficiency requirements traditionally are of relatively less importance as compared with civil passenger aircraft. Hence, impact on aeronautical and non-aeronautical military applications is evident, where weight-efficiency gains for similar types of applications can be remarkable. Aeronautical-worthy high-energy impact shielding will also enable aircraft protection against other type of menace, such as terrorist attacks.
- A high-fidelity modelling strategy to carry out virtual mechanical testing of future aeronautical structures will be developed, validated and implemented in commercial software to be used in an industrial environment. These virtual toolset will lead to better designs of the ITD’s developed within the Clean Sky 2. The industrial implementation of this strategy is also expected to have a very large impact on the design and certification of aeronautical structures, leading to faster and better designs, accelerated materials development, transformation of the engineering design optimization process and unification of design and manufacturing. In addition, high fidelity simulations will reduce the number of costly experimental tests to certify safety.
Counter Rotating Open Rotor Aircraft Concept, CROR (courtesy of AIRBUS)
REDISH project scope and workflow