Overview
The utilization of laminar flow technology is one necessary mean to further improve the eco-efficiency of future transport aircraft. Because of the different pressure distribution type and the reduced sweep of laminar wings the drag rise is encountered at lower Mach numbers and is steeper than with conventional turbulent wings. The availability of effective shock control technologies is therefore highly desired in connection with future laminar aircraft. Previous research demonstrated that shock control bumps (SCB) are a promising means to reduce the wave drag at a certain design condition at least for turbulent wings. However, SCB shapes considered so far show significant performance degradation at Mach and cl below their design condition.
The NextWing project aims on the development of effective and robust 3D shock control bumps (SCB). Novel aspects are the specific derivation of appropriate basic shapes for laminar wing pressure distributions, the reduction of negative sweep effects by dedicated shaping of the side flanks and the significant improvement of the robustness against variations of the freestream conditions. The objective is to improve the overall performance of laminar wings for typical flight mission scenarios and to significantly reduce the wave drag at high Mach. This goal shall be achieved by systematic joint numerical and experimental studies on SCB flow physics and the impact of relevant SCB properties on performance at design and off-design conditions. The project will benefit from the extensive experience of the partners in shock control and SCB design and from the availability of dedicated numerical and experimental tools developed during more than 10 years of SCB research. The outcome of the project will result in detailed design guidelines that enable the efficient design of robust 3D SCBs for arbitrary laminar aircraft configurations.
Funding
Results
New, greener wing designs
The natural laminar flow (NLF) wing concept may offer performance improvements for aircraft. An EU study helped to extend the cruise speed range of such aircraft by designing shock control bumps (SCBs) to significantly reduce the wave drag.
Meeting the aviation industry's ambitious targets for aircraft performance and efficiency requires new designs, to reduce drag and improve efficiency. Offering promise is the NLF wing, in spite of earlier and steeper transonic drag rise at high Mach numbers.
The SCB technique may greatly reduce drag in the transonic regime, though the best ways of designing robust bumps with a broad application range up to buffet onset were unknown. The EU-funded project 'Numerical and experimental shock control on laminar wing' (http://nextwing.iag.uni-stuttgart.de/ (NEXTWING)) addressed this problem. The two-member partnership aimed to provide design guidelines for SCBs under various operating conditions. They used a joint computational and experimental approach. The project ran for three years to February 2014.
Team members examined drag-reduction capabilities of SCBs, the action of bumps in buffet conditions and compiled SCB design guidelines. The examination included the fundamental flow physics affecting both scenarios.
Using a generic NLF wing results showed the possibility of designing SCBs that offer improvements in aerodynamic efficiency of swept wings. An improvement of 18 % was achieved at dash conditions of the considered wing cut, without affecting cruise performance. The result extends the flight envelope of a given wing design, applicable to swept wings and finite wings forming part of a full aircraft configuration.
Further results revealed that, at buffet conditions, certain SCB designs delay the onset of the buffet. Yet, generally, when the flow degrades the introduction of bumps exacerbates this further. The project also identified the mechanisms by which shock bumps generate stream wise vortices. In combination with further, more detailed, findings this allows the design of shock control bumps that also generate stream wise vortices without damaging the boundary layer. Such vortices may provide additional control benefits, comparable to vortex generators.
NEXTWING's results led to improved understanding of wing aerodynamics, meaning potential for improvement in efficiency and performance. Hence, the outcomes help to improve the sustainability of aviation.