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Contribution to design optimization of tiltrotor components for drag reduction

Final Report Summary - CODE-TILT (Contribution to design optimization of tiltrotor components for drag reduction)

Executive Summary:

The CODE-Tilt project was aimed at providing a methodology to be used for efficient optimization of some components of the ERICA tiltrotor fuselage, i.e. nose, wing/fuselage junction, sponsons and tail surfaces, aimed at reducing drag. To this purpose, an in-house multi-objective evolutionary algorithm was used coupled with both commercial and open-source CFD solvers. Thanks to the capability of the optimization tool used to handle multi-objective problems with multiple criteria constraints, all the constraints related to architectural/structural issues, pilot visibility, aircraft stability and controllability were properly taken into account during optimization. Finally, a series of alternative techniques to the passive design for drag minimization were thoroughly analyzed during the project, specifically the boundary layer suction/blowing on the wing/fuselage junction and the morphing wing concept on the empennages.

The obtained results are very encouraging: actually, the overall gain in drag reduction is around 8% with respect to the baseline, which is expected to lead to a significant reduction in fuel consumption as well.

Project Context and Objectives:

The CODE-Tilt project is a Call for proposal (CfP) in the framework of the CleanSky JTI, which in turn is the most ambitious aeronautical research program ever launched in Europe, essentially devoted to the identification and implementation of some breakthrough technologies aimed at improving the environmental friendliness of both fixed-wing and rotary-wing aircrafts, both in terms of noise emissions and fuel consumption.

In the Clean Sky (CS) framework, a dedicated section is devoted to rotorcraft (both helicopters and tilt-rotors), which is called Green RotorCraft (GRC). The GRC is organized in six tasks: specifically, GRC2 regards the design optimization and active flow control of both airframe and dynamic systems for drag reduction.

The CODE-Tilt project refers to CS GRC2 and is aimed at implementing and applying an innovative design methodology to be used for efficient optimization targeted to drag reduction of some components of a tiltrotor fuselage, i.e. nose, wing/fuselage junction, sponsons and tail surfaces. Effective aerodynamic design of fuselage components requires the accomplishment of multiple, and often conflicting, objectives in presence of multiple and multi-criteria constraints.

The main objectives of the projects were:

i. To set up a comprehensive and fully automatic design tool, integrating the software in use at the GRC Consortium and an in-house multi-objective optimization algorithm already developed by the University of Padova;
ii. To implement efficient and robust optimization strategies for obtainment of optimal geometries using reasonable computing times, which make them suitable for industrial purposes;
iii. To implement, test and run such tool within the industrial design procedure currently available at the GRC Consortium;
iv. To apply such tool for drag reduction of some components of a tiltrotor fuselage, i.e. nose, wing/fuselage junction, sponsons and tail surfaces, in order to improve the overall aircraft aerodynamic efficiency, while guaranteeing compliance with industrial constraints and needs.

Specifically, the wing/fuselage junction was to be optimized for drag reduction while taking into account very strict architectural/structural constraints: the target reduction on the overall aircraft drag coefficient as per the wing/fuselage junction shape modification was 0.75%. Regarding the nose, the main scope was the definition of the final optimized geometry for fuselage drag reduction without penalization of the pitching and yawing moment of the tail-off configuration and without violating pilot visibility constraints. The target value for drag reduction as per the nose shape modification was 0.7%. On the other hand, the sponson was to be optimized for drag while keeping almost unchanged the lift force with respect to the baseline and without penalization of the pitching moment of the tail-off configuration: the target value for drag reduction as per the sponson shape modification was 1.7%. Finally, as far as the empennages are concerned, the identification of an optimized empennage geometry for drag reduction (and/or aerodynamic efficiency increase) was required to be achieved in cruise flight conditions, fully compliant with stability/controllability constraints. The target value for drag reduction as per the nose shape modification was 0.4%. The overall drag reduction target on the aircraft fuselage for the components considered in the CODE-Tilt project was 3.5%.

The objectives of the project were achieved by means of a dedicated programming and simulation activity, where the software tools available at the leading industry premises for aerodynamic analyses were interfaced together and with the optimization tool proposed by the UNIPD-HIT09 Consortium. The result was a robust procedure where only the initial geometry importation and parameterization were carried out off-line, while meshing, geometrical/grid manipulation, as well as CFD analyses formed an automatic loop. The optimization tool, which is capable of efficiently handling complex multi-objective problems, was applied to review the basic fuselage components design, with the aim of minimizing any detrimental effects on drag and/or aerodynamic efficiency, through both a reliable shaping and an analysis and control of flow separations and loss mechanisms. In addition, also complementary techniques (i.e. boundary layer suction/blowing and morphing wing concepts) were considered in parallel to passive shape modifications and discussed with the leading industry. Finally, the optimized components geometry was checked for compliance with feasibility constraints in order to accomplish industrial needs for prototyping and testing.

Project Results:

See attached document.

Potential Impact:

The CODE-Tilt project is expected to result in a series of environmental benefits: in fact, drag reduction of fuselage components acts in the direction of increasing the aircraft efficiency and hence reducing fuel consumption. An overall reduction of tiltrotor fuselage drag equal to 8% is achieved. In addition, the final optimized components will be tested either in wind tunnel or in flight in the framework of GRC2, in order to verify the predicted margins of improvement.

The expected impacts can be seen as twofold: the first is product-specific, therefore "technical" and the second is more general and we shall refer to it as “social". In fact, both can have a deeper influence on the European competitiveness.

From the technical point of view, the development of a multi-objective optimization platform will have a positive impact on the reduction of the time-to-market for helicopter and aircraft industries, which will be able to develop aircraft components faster, better and cheaper, as per a reduction in the wind tunnel costs which will decrease the industrial development costs. Moreover, when optimized components will be implemented and industrialized, this will lead to more efficient vehicles having a reduced drag, which will have also a positive impact on the fuel consumption, an aspect which can be seen in direct connection to the "eco-design" concept. Referring to tiltrotors, a step toward the success of this aircraft is foreseen with the help of the present proposal. The development of more efficient and affordable tiltrotors is seen as one of the strategic plans for a decongestion in the air traffic.

All the participants in the Green Rotorcraft Consortium will benefit from CODE-Tilt, as the compiled version of the optimization toolbox will be available to each partner. The generality of the approach implemented will make it possible for aircraft industries to use the toolbox according to the specific objective functions of interest. In fact, the provision of best optimization approaches directly strengthens the competitiveness of the European aircraft industry, which is in alignment with the objectives of THEME 7 "Transportation" of the FP7.

Regarding the "social" impact, a much wider view is envisaged. The alignment of the proposal objectives is directly in accordance with “greener” pan-European transport systems for the benefit of all citizens and society and climate policy, which are declared as main drivers of the THEME 7 according to the actual work program.

Moreover, a social impact in terms of improved knowledge is expected: specifically, due to the academic nature of one of the participants, one major dissemination opportunity was given by publications. In particular, a series of scientific and promotional papers, web sites, seminars and University lessons have been carried out during the project and will be implemented after the project closure as well. The CODE-Tilt project has potential innovation impacts on the actual state of the art: both scientific journals and international conferences have been used to explain the novelties and the wide applicability of the proposed research, even in a non-aeronautical field. At the same time, this publication activity, especially conferences, has been a way of exploitation, in that other helicopter or fixed-wing aircraft manufacturers could take advantage of the adopted approach and use it directly or derive analogous methodologies.

In addition, the project achievements and knowledge have been transferred to the education of the new generation of aerospace engineers. This has enabled students to actively participate in upstream research activities and has given them the opportunity to perform applied research in cooperation with the elite of the European aeronautics industry. In addition, this has had a positive impact on recruitment of young PhD students and researchers involved in the development of advanced design methodologies for more efficient aerial vehicles. Finally, a special effort has been made to support young scientists and engineers for their training and in order to attract their interest in the topic and in flight physics in general, by holding workshops with external scientists and students.

The dissemination strategy has been intended to optimize dissemination of project knowledge to organizations that may be interested in the technological results and in the further development and/or applications of the main project achievements. To this purpose, favorable conditions will be created to facilitate exploitation even after the end of project. Specifically, with the project completion, the following main outputs are made available for further exploitation:

- Best practice approach for reliable tiltrotor fuselage simulations using advanced numerical high-fidelity tools;
- Advanced high-fidelity, multi-objective optimization procedures for enhancing tiltrotor efficiency;
- Fundamental knowledge on the design process of some critical components of the tiltrotor fuselage;
- Final assessment of the overall tiltrotor performance, including the propeller inflow effect.

As already mentioned, one of the project main strengths was that the whole optimization chain was released to the GRC Consortium at the end of the Project, following the typical rules of open source software, thus allowing end-users to access and exploit the developed tool in their research or work for free. This approach ensures that the beneficiary of the EC funding will not be limited solely to the leading industry, but the whole GRC Consortium will be able to exploit its achievements.

The delivered optimization chain includes the optimization platform in a compiled version, i.e. the GeDEA optimizer, all the interfaces with Hypermesh®, TGrid® and Fluent®, along with the pertinent theoretical and user’s guides as well as a tutorial on how to use it.

Since the project is targeted at improving efficiency of aircraft components, the user groups of the results may consist mainly of the industrial companies and research institutions of this sector. Through the final assessment phase of the project, an effective design process and the potential of multi-objective aerodynamic optimization can be exploited by GRC Consortium partners. This ensures the dissemination and exploitation of the achievements to the European aircraft industry and research community.

List of Websites:

Participating members UNIVERSITY OF PADOVA IT

HIT09 S.r.l. IT

Coordinator contact details: Ernesto Benini

Via Venezia, no.1
35131 Padova
+39 (0)49 8276767

Technical Leader contact details: Rita Ponza
Galleria Storione, no.8
35100 Padova
+39 (0)333 2900558