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European High Lift Programme II (EUROLIFT II)

Final Report Summary - EUROLIFT II (European High Lift Programme II)

The EUROLIFT II started in January 2004 under the coordination of DLR as a Specific Targeted Research Project (STREP) of the Sixth Framework Programme (FP6). The project continued the successful work of the predecessor project EUROLIFT under the leadership of Airbus-Deutschland. In view of the realisation of the demanding ecological targets of the European vision 2020, high lift systems have the potential to deliver a substantial contribution for more efficient and environmentally friendly aircraft. The general objectives were the validation of numerical and theoretical methods for the exact prediction of the aerodynamics of a complete aircraft in high-lift configuration at flight renumbers, and a numerical and experimental analysis of the physical interaction of the different vortex dominated aerodynamic effects, as well as their impact on the aerodynamic performance. This would be accomplished by using state-of-the art Reynolds averaged Navier-Stokes (RANS)-methods and also the wind tunnels European Transonic Wind Tunnel (ETW) and Low Speed Wind Tunnel (LSWT) of Airbus-Deutschland. Furthermore, an assessment of progressive high-lift systems including numerical has been conducted as well as its experimental demonstration. The research activities focus on a commercial transport aircraft configuration in various high lift settings designated as DLR F11.

The baseline model for the present studies was representative for a commercial wide-body twin-jet high lift configuration. The layout and geometry has been defined by Airbus- Deutschland, denoted as KH3Y geometry. The model was constructed and manufactured by DLR and denominated as the DLR-F11 model. The extension for the high lift configuration and the construction and manufacture of the high lift devices and nacelle has been done as part of the EUROLIFT projects. The configuration is available as a cruise model with baseline and a modified slightly drooped leading edge. The droop nose design forms the geometrical basis for all configurations of the KH3Y configuration with deployed high lift devices.

The high lift system consists of a leading edge slat and a trailing edge Fowler flap. The slat is subdivided into three parts. The elements are interconnected laterally by latches. The slat is continuously extending up to the wing tip. The local relative chord ranges from about 10 % at the inboard pressure section to nearly 24 % chord at the most outboard pressure section. The Fowler flap also consists of three parts. The first one extends up to the wing kink, and the second one up to 71 % half span. The third element extends up to the wing tip. It can be interchanged against a flaperon. For two-dimensional (2D) investigations a representative wing section at 68 % half span was selected. At this station, the slat has a local chord length of 17.7 % and the flap of 27.6 %, respectively. The high lift system can be mounted in two take-off settings and one landing setting. For the experimental investigations with respect to maximum lift analysis in EUROLIFT II, only the landing setting was considered. The flap can be mounted in several fixed window positions.

In parallel to the analysis part of the studies, a flap shape and setting optimisation was carried out in the EUROLIFT II. According to the results of the numerical optimisation, a new trailing edge flap is manufactured and wind tunnel tested in the ETW. The optimisation studies have been carried out for the KH3Y configuration in take-off setting. All experiments of the EUROLIFT projects make use of the half model test technique to benefit from the larger scale compared to full model tests. The model is mounted on a peniche. Both, fuselage as well as the peniche, incorporate labyrinth seals adjacent to each other. The effective height of the peniche and the seals in the wind tunnel amounts to 0,101 m. The high lift devices have been manufactured to fit gapless in span-wise direction for the take-off setting 2. Consequently, also the pressure sections of slat and flap are in-line with the fixed wing pressure sections for this setting. A roughness band of 5 mm width is attached to the fuselage 30 mm downstream of the fuselage. All other components are testes without any transition fixing.

The second configuration used in the EUROLIFT projects was the constant chord swept wing model AVF (Aile à Flèche Variable) of ONERA. The metal panel wing is based on a constant RA16SC airfoil section with no twist. The baseline configuration is build-up of a full span slat and Fowler flap attached on five tracks. The tracks are in line of flight for 40 degrees sweep angle. The high lift wing is equipped with 8 span-wise pressure stations with each station having 93 taps available. The wing is mounted directly on the turntable. The model is used for the analysis of transition phenomena as well as for studies on active and passive leading edge flow control.

No transition fixing was applied for these studies. Transition phenomena were detected via hot films as well as with an infrared camera. The experiments with the AFV model in EUROLIFT II have been carried out to determine the potential of active flow control to recover the slat performance. For this purpose, the model was modified to end up with a two element configuration with a retracted slat. Therefore, a new clean leading edge system consisting of six leading edge boxes incorporating a full length slot on the top surface has been designed. The slot extends parallel to the leading edge and allows constant blowing in the chord direction. The leading edge has been manufactures by Airbus-UK. The tests have been carried out in the low speed tunnel of Airbus-UK in Filton, United Kingdom. The F-LSWT is a continuous atmospheric wind tunnel with wind speeds up to 97 m/s. The closed test section has a dimension of 3.66 m x 3.05 m. Compressed air is supplied to the model utilizing the high-pressure air feed system on to the F-LSWT under-floor balance. In order to ensure that the flow control effects are not corrupted by transitional phenomena, transition fixing is applied to the upper and lower surface of the clean wing leading edge. Boundary layer measurements using a boundary layer traverse to measure boundary layer thickness downstream of the blowing slot, as well as hot-film measurements have been carried out in addition to balance and surface pressure measurements.

The project was subdivided into three major work packages (WPs). Each WP had three tasks:

- WP0 Management and coordination

- WP1 Improved validation based on EUROLIFT I data
T1.1: Geometrical model installation and deformation effects
T1.2: Boundary layer and transition impact
T1.3 Study of flap setting and modification effects
WP1, lead by DLR, covered numerical investigations which were based exclusively on existing experimental data from EUROLIFT I. Task 1.1 was coordinated by NLR. The objective was to determine wind tunnel and model installation effects. In this context, in-tunnel simulations were carried out with the KH3Y in stage 0 configuration for low and high Reynolds number tests in the B-LSWT and the ETW. Task 1.2 coordinated by ONERA, dealt with the analysis of transition phenomena based on experimental data of the EUROLIFT I project. Task 1.3 was concerned with the simulation of setting effects of the high lift devices. The task was coordinated by Airbus-Deutschland. The objective was to show the potential of CFD methods to predict 3D flap setting effects on lift and drag for model and full scale Reynolds numbers.

- WP2 Realistic high lift configurations
T2.1 Realistic aircraft configuration
T2.2 Advanced high lift design
T2.3 Novel devices for flow control
WP2, coordinated by Airbus-Deutschland, was devoted to detailed analysis and optimisation of high lift configurations. Due to its importance Task 2.1 which was also lead by Airbus-Deutschland, was subdivided into three subtasks. The first one was coordinated by Airbus-Deutschland and covered detailed flow field analysis on the three complexity stages of the KH3Y high lift configuration in the BLSWT for low Reynolds number conditions. Complementary to the experimental and numerical analysis activities in Task 2.1 Task 2.2 addressed the topic of numerical optimisation of high lift configurations. The common activity, which was coordinated by DLR, focused on the setting and shape optimisation of a 2D section of the KH3Y wing / fuselage configuration without engines. Task 2.3 coordinated by Airbus-UK, has been introduced to assess the potential of an active flow control concept on a multi-element wing configuration when replacing the slat. The task consisted of preparatory numerical investigations and a demonstration test using the accordingly modified AFV configuration in the F-LSWT. An evaluation of the amount of required bleed air compared to the performance gain has been carried out to assess the feasibility of this flow control approach based on constant blowing.

- WP3 Methods and tools
T3.1 Transition prediction
T3.2 Numerical methods
T3.3 Experimental transition and deformation detection
WP3, coordinated by ONERA, addressed the aspect of further developing numerical as well as experimental tools for high lift simulations. Task 3.1 also led by ONERA, was closely linked to the Task 1.2 activities. It focused on the extension of methods for transition prediction from 2.5D (EUROLIFT I activity) to 3D flow fields based on database methods and on local theory approaches. Task 3.2 intended to improve areas in the numerical simulation, that have been identified as the most promising for accuracy and efficiency improvement within the RANS codes applied. These areas are turbulence modelling and mesh generation. The focus of Task 3.3 was finally on improved experimental techniques for transition and deformation detection for cryogenic test conditions. The task was coordinated by ETW. Transition detection was accomplished using and assessing hot wire and hot film arrays in the ETW pilot facility, while the detection of wing deformation was done by using the enhanced stereo pattern technique (ESPT) for the tests with the KH3Y model in the ETW.

The EUROLIFT II project has addressed a variety of issues considered essential for the successful experimental and numerical simulation of high lift commercial aircraft configurations. One of the most important issues is the capability of RANS methods to predict maximum lift determining effects and their Reynolds-number dependency on complex configurations with deployed high lift devices. A comprehensive validation database for high lift commercial aircraft configurations has been generated covering low as well as flight representative Reynolds-numbers. Maximum lift determining effects could be isolated by investigating configurations of different complexity levels. The experimental studies are accompanied by extensive CFD studies making use of various hybrid-unstructured as well as structured grid codes. Whereas these studies have been carried out assuming fully turbulent free air flow, dedicated investigations are devoted to identify the influence of wind tunnel walls and model mounting effects deemed necessary to assess the impact of these effects for the reliable validation of the RANS codes. Numerical optimisation of the shape and setting of a trailing edge flap is also addresses in the project. The resulting optimised flap shape has been tested under cryogenic conditions in order to verify the aerodynamic potential of the numerical optimisation. Studies on transition phenomena, transition location prediction, as well as investigations on physical modelling and grid generation approaches complete the range of topics, which is covered by the EUROLIFT II project. The experimental database and the numerical results and experience gathered in the project including the areas of code improvement will be the basis to approach the final target of the predicting maximum lift on a complex high lift configuration with a pre-defined high accuracy.