Final Report Summary - DREAM-TILT (Assessment of tiltrotor fuselage drag reduction by wind tunnel tests and CFD)
Executive Summary:
The DREAm-TILT project was focused on the assessment of drag reduction achieved through the aerodynamic optimization of some critical components of the ERICA tiltrotor fuselage. This was accomplished both from an experimental and a numerical point of view.
Specifically, a CFD-based optimization activity was previously carried out in GRC2 by University of Padova and HIT09 S.r.l. in order to reduce the drag levels of some specific components of the reference tiltrotor configuration, and proper shapes of some fuselage components (i.e. wing/fuselage junction, wing/nacelle junction, nose, landing gear sponson and empennage) were identified, that contribute to reduce aircraft drag and enhance aerodynamic efficiency. In particular, 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 as well during optimization. The numerically obtained results from optimization were very encouraging: actually, the overall predicted gain in drag reduction was around 8% with respect to the baseline (without taking into account rotor blade stubs effects), which is expected to lead to a significant reduction in fuel consumption as well.
In DREAm-TILT, the benefits obtained from the aerodynamic optimization in terms of drag reduction were first thoroughly assessed through a dedicated wind tunnel campaign: specifically, the final optimized fuselage was tested and the drag reduction with respect to the original configuration determined achieving a drag reduction of 4.5% (including rotor blade stubs effects). All the optimized components were tested sequentially with the aim of getting an accurate drag breakdown and identifying the contribution of each component to the overall aerodynamic performance of the fuselage. Additional classical flow visualization runs and infrared thermography were finally carried out to enhance knowledge on the transition and separation regions for the different drag reduction configurations.
In parallel, a CFD activity was carried out on both the model scaled aircraft tested in the wind tunnel and the full scale aircraft in order to evaluate rotor effects and the full scale (Mach dependent) characteristics. In a first phase, a series of blind test simulations at wind tunnel conditions were performed for both basic and optimized configurations of the scaled model. In a second stage, the numerical results on both the baseline and optimized ERICA geometries were compared and fully validated against the acquired wind tunnel data. Finally, the numerical models already tested and validated were used for the assessment of the aerodynamic performance of the optimized ERICA fuselage at full scale conditions (Mach = 0.58) including the rotor effects.
Overall drag reduction obtained by CFD on the scaled model at optimization attitude was around 4%, while it was equal to 4.5% at full scale conditions. Numerical results are in good agreement with wind tunnel data and the initial drag reduction target required by GRC (-3.5%) was definitely achieved and overcome.
Project Context and Objectives:
The DREAm-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 DREAm-Tilt project supports this effort trough experimental tests and numerical simulations aimed at assessing the aerodynamic efficiency of tiltrotor fuselage components.
Considering all the operational modes for a tiltrotor, among the major drag sources are the front fuselage, the wing/fuselage fairings, the landing gear sponsons and the rear empennages. In GRC2 University of Padova and HIT09 had already identified properly optimized shapes of these components that contribute to decreasing aircraft drag and enhancing aerodynamic efficiency. To this purpose, Computational Fluid Dynamics (CFD) coupled with innovative design methodologies based on multi-objective evolutionary algorithms were used. Through wind tunnel tests, DREAm-Tilt was aimed at assessing the optimized fuselage components of future European civil tiltrotors based on ERICA architecture and determining drag reduction with respect to the baseline configuration.
The main objectives of the projects were:
i) to test in the wind tunnel both the baseline and optimized tiltrotor fuselage components;
ii) to assess experimentally the benefit of shape optimization in terms of drag reduction;
iii) to derive experimentally an accurate drag breakdown and identify the contribution of each optimized component to the overall aerodynamic performance of the fuselage;
iv) to assess via CFD simulations both the baseline and optimized tiltrotor geometry in wind tunnel flow conditions and identify accurate numerical models, including laminar/turbulent transition;
v) to validate numerical models against wind tunnel data;
vi) to assess via CFD simulations the optimized tiltrotor geometry in full scale conditions including rotor effects.
In order to achieve these objectives, a wind tunnel test campaign was conducted on a power-off model of the isolated ERICA tiltrotor fuselage for both the baseline and optimized configurations. During the experimental campaign, all the optimized components were tested sequentially to get an accurate drag breakdown and identify the contribution of each component to the overall fuselage aerodynamic performance. In addition, the project carried out additional flow visualization runs to enhance knowledge on the transition and separation regions for the different drag reduction configurations.
In parallel, suitable CFD models for both configurations were assessed as well and then numerical models were validated against wind tunnel data. In a second stage, a series of calculations at full scale conditions were carried out using the numerical models validated against wind tunnel data to assess the impact of shape optimization at real operating flight conditions and including also rotor effects. The CFD calculations were run using both the commercial s/w ANSYS Fluent® and the open-source CFD code OpenFOAM®: this was done with the aim of verifying the applicability of the latter on complex geometries, since it could be profitably used by the GRC Consortium without affording any licensing costs.
The overall drag reduction target on the aircraft fuselage for the components considered in the DREAm-Tilt project was 3.5%. In addition, drag reduction was required to be achieved while fulfilling a series of constraints (architectural/structural constraints) and without penalizing other aircraft characteristics (like for instance aerodynamic efficiency, stability and controllability characteristics, pilot visibility).
Project findings are paving the way to design of a more environmentally friendly tiltrotor. In fact, decreasing fuselage drag should have major positive implications in terms of efficiency and fuel consumption.
Project Results:
See attached document.
Potential Impact:
The DREAm-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 around 4.5% was calculated and verified in the wind tunnel. Testing of the optimized components in wind tunnel made it possible to verify the predicted margins of improvement. Actual quantification of benefits in terms of fuel saving has not yet been carried out being out of the scope of the project but it will be estimated within GRC2.
In addition, a more general outcome of the DREAm-TILT project deals with the application of multi-objective evolutionary optimization techniques coupled with CFD tools, that have been demonstrated during the project to be mature enough for product application (excellent agreement with wind tunnel results reinforces the confidence in the numerical design tool): actually, TRL4 was achieved. In fact, these kind of techniques begin to be quite widespread in the aeronautical community, but they often remain stick to a numerical level, and very rare are the cases where their effectiveness has been demonstrated directly through experiments. Actually, DREAm-TILT goes exactly in this direction, and it has demonstrated that these tools, especially when applied since the very early stages of the aircraft design, could be a valuable support to an optimal design, thus reducing experimental and development costs.
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, an improved knowledge on the aerodynamic behavior of some optimized components of the tiltrotor fuselage will be useful for the future development of such an aircraft and will give some important guidelines for development of more efficient aircraft components, which could be implemented 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 project. The development of more efficient and affordable tiltrotors is seen as one of the strategic plans for a decongestion in the air traffic and it will directly strengthen the competitiveness of the European aircraft industry, which is in alignment with the objectives of THEME 7 "Transportation" of the FP7.
Actually, regarding the exploitation of results, not only the applicants and the leading industry (i.e. AgustaWestland) will benefit from the outcomes of DREAm-Tilt. In fact, the generality of the implemented approach will make it possible for aircraft industries to use the optimization toolbox and adopt best practice approach for aircraft design according to the specific objective functions of interest. Also the provision of best optimization approaches acts in the direction of enhancing the competitiveness of the European aircraft industry.
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 which will be implemented in both scientific and promotional papers, web sites, seminars and University lessons. These dissemination activities have been carried out during the project and will be implemented after the project closure as well. The DREAm-TILT project has potential innovation impacts on the actual state of the art: both scientific journals and international conferences will be 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 and will be a way of exploitation even after the project closure, 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, thanks to the academic nature of one of the participants, 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 design using multi-objective, multi-disciplinary automated optimization tools;
- Best practice approach for reliable tiltrotor fuselage simulations using advanced numerical high-fidelity tools;
- Best practice approach for reliable tiltrotor fuselage wind tunnel tests for drag assessment;
- Fundamental knowledge on the design process of some critical components of the tiltrotor fuselage;
- Final assessment of the overall tiltrotor performance at full scale flight conditions, including the propeller inflow effect;
- Multi-objective evolutionary optimization+CFD codes as a mature tool for product application (TRL 4).
It is worth remembering that the whole optimization chain was already released to the GRC Consortium at the end of a previous CfP (namely, CODE-Tilt), 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.
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
HIT09 S.r.l. IT
UNIVERSITY OF PADOVA IT
RUAG Aviation CH
Coordinator contact details: Rita Ponza
Piazzetta Bettiol, no.15
35137 Padova- Italy
+39 3332900558
r.ponza@hit09.com
Contact person University of Padova: Ernesto Benini
Via Venezia, no.1
35131 Padova - Italy
+39 (0)49 8276767
ernesto.benini@unipd.it
Contact person RUAG Aviation: Andreas Hauser
Schiltwaldstrasse
6032 Emmen · Switzerland
+41 412683829
andreas.hauser@ruag.com
The DREAm-TILT project was focused on the assessment of drag reduction achieved through the aerodynamic optimization of some critical components of the ERICA tiltrotor fuselage. This was accomplished both from an experimental and a numerical point of view.
Specifically, a CFD-based optimization activity was previously carried out in GRC2 by University of Padova and HIT09 S.r.l. in order to reduce the drag levels of some specific components of the reference tiltrotor configuration, and proper shapes of some fuselage components (i.e. wing/fuselage junction, wing/nacelle junction, nose, landing gear sponson and empennage) were identified, that contribute to reduce aircraft drag and enhance aerodynamic efficiency. In particular, 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 as well during optimization. The numerically obtained results from optimization were very encouraging: actually, the overall predicted gain in drag reduction was around 8% with respect to the baseline (without taking into account rotor blade stubs effects), which is expected to lead to a significant reduction in fuel consumption as well.
In DREAm-TILT, the benefits obtained from the aerodynamic optimization in terms of drag reduction were first thoroughly assessed through a dedicated wind tunnel campaign: specifically, the final optimized fuselage was tested and the drag reduction with respect to the original configuration determined achieving a drag reduction of 4.5% (including rotor blade stubs effects). All the optimized components were tested sequentially with the aim of getting an accurate drag breakdown and identifying the contribution of each component to the overall aerodynamic performance of the fuselage. Additional classical flow visualization runs and infrared thermography were finally carried out to enhance knowledge on the transition and separation regions for the different drag reduction configurations.
In parallel, a CFD activity was carried out on both the model scaled aircraft tested in the wind tunnel and the full scale aircraft in order to evaluate rotor effects and the full scale (Mach dependent) characteristics. In a first phase, a series of blind test simulations at wind tunnel conditions were performed for both basic and optimized configurations of the scaled model. In a second stage, the numerical results on both the baseline and optimized ERICA geometries were compared and fully validated against the acquired wind tunnel data. Finally, the numerical models already tested and validated were used for the assessment of the aerodynamic performance of the optimized ERICA fuselage at full scale conditions (Mach = 0.58) including the rotor effects.
Overall drag reduction obtained by CFD on the scaled model at optimization attitude was around 4%, while it was equal to 4.5% at full scale conditions. Numerical results are in good agreement with wind tunnel data and the initial drag reduction target required by GRC (-3.5%) was definitely achieved and overcome.
Project Context and Objectives:
The DREAm-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 DREAm-Tilt project supports this effort trough experimental tests and numerical simulations aimed at assessing the aerodynamic efficiency of tiltrotor fuselage components.
Considering all the operational modes for a tiltrotor, among the major drag sources are the front fuselage, the wing/fuselage fairings, the landing gear sponsons and the rear empennages. In GRC2 University of Padova and HIT09 had already identified properly optimized shapes of these components that contribute to decreasing aircraft drag and enhancing aerodynamic efficiency. To this purpose, Computational Fluid Dynamics (CFD) coupled with innovative design methodologies based on multi-objective evolutionary algorithms were used. Through wind tunnel tests, DREAm-Tilt was aimed at assessing the optimized fuselage components of future European civil tiltrotors based on ERICA architecture and determining drag reduction with respect to the baseline configuration.
The main objectives of the projects were:
i) to test in the wind tunnel both the baseline and optimized tiltrotor fuselage components;
ii) to assess experimentally the benefit of shape optimization in terms of drag reduction;
iii) to derive experimentally an accurate drag breakdown and identify the contribution of each optimized component to the overall aerodynamic performance of the fuselage;
iv) to assess via CFD simulations both the baseline and optimized tiltrotor geometry in wind tunnel flow conditions and identify accurate numerical models, including laminar/turbulent transition;
v) to validate numerical models against wind tunnel data;
vi) to assess via CFD simulations the optimized tiltrotor geometry in full scale conditions including rotor effects.
In order to achieve these objectives, a wind tunnel test campaign was conducted on a power-off model of the isolated ERICA tiltrotor fuselage for both the baseline and optimized configurations. During the experimental campaign, all the optimized components were tested sequentially to get an accurate drag breakdown and identify the contribution of each component to the overall fuselage aerodynamic performance. In addition, the project carried out additional flow visualization runs to enhance knowledge on the transition and separation regions for the different drag reduction configurations.
In parallel, suitable CFD models for both configurations were assessed as well and then numerical models were validated against wind tunnel data. In a second stage, a series of calculations at full scale conditions were carried out using the numerical models validated against wind tunnel data to assess the impact of shape optimization at real operating flight conditions and including also rotor effects. The CFD calculations were run using both the commercial s/w ANSYS Fluent® and the open-source CFD code OpenFOAM®: this was done with the aim of verifying the applicability of the latter on complex geometries, since it could be profitably used by the GRC Consortium without affording any licensing costs.
The overall drag reduction target on the aircraft fuselage for the components considered in the DREAm-Tilt project was 3.5%. In addition, drag reduction was required to be achieved while fulfilling a series of constraints (architectural/structural constraints) and without penalizing other aircraft characteristics (like for instance aerodynamic efficiency, stability and controllability characteristics, pilot visibility).
Project findings are paving the way to design of a more environmentally friendly tiltrotor. In fact, decreasing fuselage drag should have major positive implications in terms of efficiency and fuel consumption.
Project Results:
See attached document.
Potential Impact:
The DREAm-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 around 4.5% was calculated and verified in the wind tunnel. Testing of the optimized components in wind tunnel made it possible to verify the predicted margins of improvement. Actual quantification of benefits in terms of fuel saving has not yet been carried out being out of the scope of the project but it will be estimated within GRC2.
In addition, a more general outcome of the DREAm-TILT project deals with the application of multi-objective evolutionary optimization techniques coupled with CFD tools, that have been demonstrated during the project to be mature enough for product application (excellent agreement with wind tunnel results reinforces the confidence in the numerical design tool): actually, TRL4 was achieved. In fact, these kind of techniques begin to be quite widespread in the aeronautical community, but they often remain stick to a numerical level, and very rare are the cases where their effectiveness has been demonstrated directly through experiments. Actually, DREAm-TILT goes exactly in this direction, and it has demonstrated that these tools, especially when applied since the very early stages of the aircraft design, could be a valuable support to an optimal design, thus reducing experimental and development costs.
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, an improved knowledge on the aerodynamic behavior of some optimized components of the tiltrotor fuselage will be useful for the future development of such an aircraft and will give some important guidelines for development of more efficient aircraft components, which could be implemented 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 project. The development of more efficient and affordable tiltrotors is seen as one of the strategic plans for a decongestion in the air traffic and it will directly strengthen the competitiveness of the European aircraft industry, which is in alignment with the objectives of THEME 7 "Transportation" of the FP7.
Actually, regarding the exploitation of results, not only the applicants and the leading industry (i.e. AgustaWestland) will benefit from the outcomes of DREAm-Tilt. In fact, the generality of the implemented approach will make it possible for aircraft industries to use the optimization toolbox and adopt best practice approach for aircraft design according to the specific objective functions of interest. Also the provision of best optimization approaches acts in the direction of enhancing the competitiveness of the European aircraft industry.
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 which will be implemented in both scientific and promotional papers, web sites, seminars and University lessons. These dissemination activities have been carried out during the project and will be implemented after the project closure as well. The DREAm-TILT project has potential innovation impacts on the actual state of the art: both scientific journals and international conferences will be 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 and will be a way of exploitation even after the project closure, 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, thanks to the academic nature of one of the participants, 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 design using multi-objective, multi-disciplinary automated optimization tools;
- Best practice approach for reliable tiltrotor fuselage simulations using advanced numerical high-fidelity tools;
- Best practice approach for reliable tiltrotor fuselage wind tunnel tests for drag assessment;
- Fundamental knowledge on the design process of some critical components of the tiltrotor fuselage;
- Final assessment of the overall tiltrotor performance at full scale flight conditions, including the propeller inflow effect;
- Multi-objective evolutionary optimization+CFD codes as a mature tool for product application (TRL 4).
It is worth remembering that the whole optimization chain was already released to the GRC Consortium at the end of a previous CfP (namely, CODE-Tilt), 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.
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
HIT09 S.r.l. IT
UNIVERSITY OF PADOVA IT
RUAG Aviation CH
Coordinator contact details: Rita Ponza
Piazzetta Bettiol, no.15
35137 Padova- Italy
+39 3332900558
r.ponza@hit09.com
Contact person University of Padova: Ernesto Benini
Via Venezia, no.1
35131 Padova - Italy
+39 (0)49 8276767
ernesto.benini@unipd.it
Contact person RUAG Aviation: Andreas Hauser
Schiltwaldstrasse
6032 Emmen · Switzerland
+41 412683829
andreas.hauser@ruag.com
