New Methodologies Tailored for the design of Aerodynamically Robust Laminar Wings

Kurzfassung

The present work reports on the progress recently made in methodologies for robust laminar wing design. Here robustness means reserves in the design that allow for acceptable off-design performance qualities by keeping the wing laminar over a wide range of flight conditions. This is achieved by combining new methodologies with experience and knowledge obtained with traditional laminar wing design methods. The first part of this work deals with the design of a transonic Natural Laminar Flow (NLF) wing for a new short range aircraft. In the first step, a transonic NLF airfoil catalogue is build up using a new sectional conical wing method which allows the design of transonic wing sections taking into account the effects of sweep and taper for the computational cost of a classical 2D method. Application of the catalogue leads to a 3D wing with an acceptable large region with laminar boundary layer and small shocks at design and specified off-design conditions. Comparing the wing designed using conical wing sections to the same configuration with turbulent boundary layer the total drag can be reduced by 10.7%. This illustrates the usefulness of the conical design method. The second part of this work deals with an Automated Target Pressure Generator (ATPG). The ATPG provides input to inverse airfoil and wing design methods. The generator optimises the pressure distributions in terms of minimising drag while keeping certain boundary conditions constant, e.g. lift and momentum. Both NLF and Hybrid Laminar Flow (HLF) type pressure distributions can be considered including suction distribution design. Regarding robust designs the transition positions are well defined and conservatively predicted by applying an offset. Using the ATPG the NLF design could be further improved by introducing a HLF panel over the inboard wing and thus reducing the total drag by 12.9% compared to its fully turbulent configuration.