GREen Turboprop Experimental Laminar Flow Wind Tunnel Testing

Project Information

GRETEL

Grant agreement ID: 737671

DOI

10.3030/737671

Project closed

EC signature date 21 August 2017

Start date 1 February 2017

End date 31 March 2022

Funded under

• SOCIETAL CHALLENGES - Smart, Green And Integrated Transport

Total cost

€ 2 765 151,15

EU contribution

€ 2 248 203,63

Coordinated by

PANEPISTIMIO PATRON
Greece

Periodic Reporting for period 5 - GRETEL (GREen Turboprop Experimental Laminar Flow Wind Tunnel Testing)

Reporting period: 2020-12-01 to 2022-03-31

Summary of the context and overall objectives of the project

GRETEL project, as part of the R-IADP, contributes to the objectives of increased fuel efficiency and noise reduction through the realisation of a large scale natural laminar flow, flexible wing model, with integrated innovative morphing active devices that will be verified and eventually tested in a large Wind Tunnel (WT). The proposed activities will mature the Technology Readiness Level (TRL) up to 6 and drastically de-risk the integration of the investigated solutions on future products, effectively resulting in reducing the direct operating costs for the airlines and minimizing the impact on the environment.
Morphing structures allow a shape change without the generation of discontinuities, in other words without aerodynamic gaps. Past research in this area usually focused either on aerodynamic performance or system integration, with relatively little attention on the strict requirements imposed by the long lifetimes and extreme environmental conditions the structural materials are exposed to.
The technological improvements have positive impacts on all the items contributing to the total cash operating costs such as fuel burn reduction, reduced maintenance costs, reduced navigation, and airport fees due to structural weight saving (innovative aircraft architectures and lighter materials utilization). The technological enhancements have a significant appeal also on the passengers that can enjoy a better air travel experience thanks to higher comfort and lower noise levels. All these benefits and economic advantages will be even more evident for regional turboprop aircraft that are typically less expensive to operate than the regional jets.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

During the first period, the first design requirements were set. The aim of the model is to ensure a correct simulation of flow and forces on the wing. For this reason, it will be capable of simulate stiffness of real wing by the means percent deformation at wing tip in terms of vertical deflection and airfoil chord rotation.
During the second period, the preliminary design review took place. An iterative process for the wing’s stiffness calculation and mass distribution was also developed using optimization algorithms. A scaled wing was proposed relative the flight profile and the scaling methodology in order to achieve the goal results for the final wing tunnel model.
During the third period, the project moved to the detailed design. Based on test matrix and wind tunnel test requirements, the safety margins of all structural parts were calculated, while ensuring it is flutter free for the velocities considered, allowing definition of mechanical interfaces with the wing tunnel test facility and morphing devices.
Based on this dimensioning, a first iteration of a Manufacturing-Assembly-Integration plan has been completed and a proposal for wing test model instrumentation was completed. The GRETEL CFRP Wing structure was subjected to a “build-to-print”-approach.
During the fourth period, activities were focused on manufacturing and integration activities. Special attention was drawn to the optimal instrumentation method in terms of accuracy and manufacturability, cable and pipe routing. Additionally, a verification strategy was followed to ensure proper tolerancing and surface quality for laminar flow requirements.
In the fifth period, ground and vibration tests had been performed. to ensure that the design and modeling assumptions are valid. Support during model installation was provided by means of installation steps in the wind tunnel facilities and close collaboration (including physical presence) with wind tunnel operator concerning the installation and removal of the morphing devices. GRETEL provided test data and instrumentation concerning the deformations experienced by the wing during testing.
GRETEL will serve as a case study showcasing manufacturing and material expertise of a model of such a size, improve ground vibration testing for future programs, transfer knowledge via education on utilization and expansion of the aeroelastic optimization techniques and publish the results to strengthening European collaboration in digitization of aircraft design process.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The innovations within GRETEL have strong technical impacts regarding the knowledge about highly integrated lightweight morphing – adaptive wing structures. These innovations contribute towards a realization of a dependable and lightweight aircraft wing system that meet the Regional and Large Passenger Aircraft IADP objectives for system flight test campaign. The project utilized advanced aerodynamic and aeroelastic design tools that allowed simultaneous aerodynamic and structural analysis – optimization, optimal wing geometry throughout all flight regimes (morphing wing design). This capability is expected to enable reduction of development time and consequently reduction of development costs.
The solutions developed in GRETEL focus on the importance of structural integration, which is the main limiting factor in the industrial and economical exploitation of conformal morphing. This delivered direct impacts for next generation aircrafts development increase knowledge on flow enhancement and control technologies implementation, enable new breakthrough design approaches for composite aircraft fleets and confirm the testing feasibility of a highly integrated flexible wing model through Wind Tunnel Testing.
The ecological impact of the GRETEL project is mainly on increasing aerodynamic efficiencythrough the realization of novel wing structures with enhanced aerodynamic efficiency. These, in turn, are expected to offer significantly reduced in field fuel consumption.
Overall, GRETEL technological and innovative methodologies with respect to design, analysis, manufacturing, and integration of morphing devices supports the 2050 objectives of the European Commission for the aviation industry: reduce CO2 by 75% and NOx emissions by 90%.
In terms of socio-economic impact, regional aviation plays a very important role in contemporary air transports. Currently non-European actors lead the growing regional aircraft market. To increase the market share for European manufacturers, technological developments and innovation are required to improve the competitiveness of the offered products. To be competitive on the European market, cost-effectiveness and environmental aspects must be covered.
According to various studies, around 30% of all passengers are travelling short distances of 500km or less. On these routes a turboprop aircraft (like addressed via GRETEL) requires only about half of the fuel compared with a jet while the duration of flight is nearly the same. Equipped with innovative techniques to further decrease fuel consumption this re-opens the path for turboprop machines.
Looking from a market perspective, one of the major impacts of the GRETEL project is the reinforcement of the competitiveness of Europe’s aircraft industry and European aircraft operators. This is in full alignment with the European Union strong focus on innovation as a basis for societal growth and prosperity, as well as the emphasis placed on the R&D impact on job creation, societal growth and investment associated with the creation of a strong industrial base and on reducing the environmental impact of technology in line with a forward-looking climate change policy.

Project poster