Concept and Objectives:
AFLoNext is a four year EC L2 project with the objective of proving and maturing highly promising flow control technologies for novel aircraft configurations to achieve a quantum leap in improving aircraft’s performance and thus reducing the environmental footprint. The project consortium is composed by forty European partners from fifteen countries. The work has been broken down into seven work packages. The AFLoNext concept is based on six Technology Streams:
(1) Hybrid Laminar Flow technology applied on fin and wing for friction drag reduction.
(2) Flow control technologies applied on outer wing for performance increase.
(3) Technologies for local flow separation control applied in wing/pylon junction to improve the performance and loads situation mainly during take-off and landing.
(4) Technologies to control the flow conditions on wing trailing edges thereby improving the performance and loads situation in the whole operational domain.
(5) Technologies to mitigate airframe noise during landing generated on flap and undercarriage and through mutual interaction.
(6) Technologies to mitigate/control vibrations in the undercarriage area during take-off and landing.
AFLoNext aims to prove the engineering feasibility of the HLFC technology for drag reduction on fin in flight test and on wing by means of large scale testing as well as for vibrations mitigation technologies for reduced aircraft weight and for noise mitigation technologies.
The peculiarity of the AFLoNext proposal in terms of holistic technical approach and efficient use of resources becomes obvious through the joint use of a flight test aircraft as common test platform for the above mentioned technologies.
To improve aircraft performance locally applied active flow control technologies on wing and wing/pylon junction are qualified in wind tunnels or by means of lab-type demonstrators.
AFLoNext Results in brief:
The aim of HLFC technology is to achieve laminar flow with the help of a suction system to reduce the friction drag on the aircraft. The implementation of a suction system, however, adds additional weight, diminishing the fuel-burn benefit. The structural design of the HLFC systems for vertical tail plane and wing must be done with great care. Using the simplified suction approach originating from the ALTTA project as our guide, we plan to minimize the structure and its weight as much as possible. The application of HLFC for the fin belongs to work package 1.1, and for the wing, to WP1.2.
For the design envelope we have to distinguish between two types of flight case: first, those for which we expect the simplified suction system has to work properly, i.e. to produce laminar flow on both sides of the VTP, and, second, those with maximal loads, for which it is important to size the structural layout. The flight cases of the second type will cause deformations of the VTP box which produce high stresses at the connection of the HLFC leading edge to the front spar of the VTP box. A finite element calculation of these stresses showed that pure or grade-2-titanium can be used for manufacturing. This is beneficial, because sheets out of this material can be cold-formed, thus using manufacturing processes already planned. Cold-forming is not possible for the titanium alloy Ti6Al4V or grade-5-titanium which is most commonly used for aerospace applications.
One outcome of the PDR for the design of the HLFC leading edge was that the SONACA concept based on super plastic forming and diffusion bonding of the titanium alloy Ti6Al4V was selected for the ground-based demonstrator. The review initiated some modifications of the size and distribution of the chambers, as well as an art movement of the front spar to meet the segregation rules for the leading edge of an aircraft. Furthermore, the original system design with only one duct was changed into a design with two ducts; one for the supply of the bleed air for the wing ice protection system and a separate one for the air sucked through the micro-perforation.
Active Flow Control investigations are applied to two different but complementary design parts: the wing/pylon region when integrating modern-type High By-pass Ratio engines, and the outer region of aggressive wing-tip extension.
The WP3 for control means for vibration and aeroelastic coupling focused in the second period mainly on the ground vibration test. The ground vibration test was successfully completed. The results were needed to update the finite element model.
WP4 is divided in the activities on landing gear/flap interaction noise and the porous flap side edge investigations. The overall objectives of WP4 in the second reporting period were the design of an add-on treatment for landing gear noise reduction, wind tunnel testing of low noise landing gear devices and wind tunnel test on an Airbus-type porous flap side edge, and lastly initiating the flight test preparation and related design work for both, landing gear and flap side edge.
Multifunctional trailing edge concepts objectives are to investigate trailing-edge flow control devices that are multi-functional i.e. those that can be used at low and high speed and/or for the control of different aerodynamic phenomenon, the use of numerical analysis to study the potential aerodynamic benefits of a variety of trailing-edge devices, such as fluidic Gurney flaps, and therefore determine the key design and performance requirements of such devices.
Krüger design for an HLFC wing
Wild, Jochen; Franke, Dirk M.2015
Aerodynamic Design of a Folded Krüger Device for a HLFC Wing
Franke, Dirk M.; Wild, Jochen2014
Designing and Testing Active Flow Control Systems at the Junction of Ultra-High Bypass Ratio Engines and the Wing
Meyer, Michael; Lengers, Matthias; Bieler, Heribert; Fricke, Sebastian; Wild, Jochen; Norman, David2014