Martin Kruse

The DLR Project LamAiR: Design of a NLF Forward Swept Wing for Short and Medium Range Transport Application

The LamAiR (Laminar Aircraft Research) project deals with the design of a laminar wing for short and medium range transport aircraft operated in the transonic regime. It is well known that extensive laminar flow on wings of such aircraft still can be achieved by natural means, i.e. solely by contour shaping of the airfoil sections. But with Reynolds numbers being in the order of 25 millions in cruise condition the leading edge sweep of the wing should not be higher than approximately 20deg in order to limit the growth of cross-flow instabilities and, hence, prevent early transition. Consequently, the design cruise Mach number for laminar wings of conventionally aft-swept configurations cannot exceed values of about 0.75 and it is expected that the high-speed off-design performance is rather poor. Within the DLR project LamAiR it is therefore investigated if these aerodynamic shortcomings can be overcome by employing forward sweep in combination with aeroelas-tic tailoring using CFRP (Carbon Fiber Reinforced Plastics) materials. In particular the goal is to design a forward swept laminar wing having a design Mach number of 0.78 and the capability of reaching Mach 0.80 in high-speed off-design. The present paper gives an overview on the current status of the project as well as prospects for future work.

A Conceptual Study of a Transonic NLF Transport Aircraft with Forward Swept Wings

DLR’s concept for a natural laminar flow transonic transport aircraft with forward swept wings is presented. Giving an overview on the aircraft’s configurational layout first, the focus is on the multidisciplinary design of NLF wing and its aerodynamic performance. Results from high-fidelity coupled aero-structural simulations show that a significant extent of laminar flow is achievable. Torsional divergence of the wing is successfully suppressed by aeroelastic tailoring. The impact of elastic wing deformation on boundary layer stability and NLF performance is studied. Finally, results of the aircraft’s cruise performance and expected fuel savings are provided and compared to results from preliminary design.

Insect Contamination Impact on Operational and Economic Effectiveness of Natural-Laminar-Flow Aircraft

The objective of this paper is to investigate the effect of insect contamination on operational and economic effectiveness of an aircraft with natural laminar flow wings designed by DLR. It is intended to show how insect debris located close to the wing leading edge influence fuel consumption on single missions as well as economic metrics like net present value. The focus will be on short-to-medium haul operations, i.e., aircraft similar to current state-of-the-art 150 passenger seated aircraft. During the analysis process tools for aircraft design, mission simulation and computation, insect contamination as well as life-cycle cost assessment will be used. The overall goal is to provide aircraft operators with a better understanding of the operational behavior of natural laminar flow aircraft under realistic operational boundary conditions and related economic implications.

Determination of the Critical Cross Flow N-factor for the Low-Speed Wind Tunnel Braunschweig (DNW-NWB)

In order to determine the critical cross flow N-factor for DNW-NWB wind tunnel, transition experiments are conducted on a 3D-wing model. Infrared thermography is used to detect spanwise the transition line at various angles of attack and Reynolds numbers. The obtained transition lines are then prescribed in RANS flow simulations of the experiment. Calculated boundary layer data of laminar regions serves directly as input for a subsequent analysis of boundary layer stability. Employing local linear stability analysis, critical N-factors are attained at the transition location for each inviscid streamline. A 2-N-factor method is used for individual treatment of Tollmien-Schlichting and cross flow instability. From the broad variety of observed transition scenarios, cross flow dominated cases are filtered. Those are used to calculate an uncertainty weighted mean value of the critical cross flow N-factor for NWB facility. The results show NCFcrit to be in the range of 7.4–9.3. Remaining scatter and a noticeable dependency of NCFcrit to the surface side of the model are likely to be related to methodological shortcomings of the eN method.

Comparison of Breguet and ODE Evaluation of the Cruise Mission Segment in the Context of High-Fidelity Aircraft MDO

This report presents a multi-disciplinary optimization (MDO) process that minimizes the mission fuel burn of an aeroelastic long-range transport aircraft configuration, by modifying the wing planform, twist, and structural element thicknesses. Two optimizations are performed, one where the fuel burn is approximately evaluated through Breguet range equation, and the other where the ordinary differential equation (ODE) for the step-climb cruise is formally integrated. This is done in order to determine if the Breguet equation is still sufficient in face of high-fidelity aeroelastic simulations. The two optimized designs ended up having similar improvements, thus confirming the applicability of the Breguet equation, for the number of design parameters that were employed.