Aerodynamic Design and Analysis of HLFC Wings within the European Project HLFC-WIN

Abstract

Results for the numerical aerodynamic design and analysis of a long-range, large passenger aircraft equipped with a Hybrid Laminar Flow Control (HLFC) system are presented. This work was performed within the European project HLFC-WIN. The reference geometry of this study is the long-range cruise Airbus research XRF1 geometry, designed for turbulent flow. The HLFC part of the wing is restricted to an outer wing region which extends from the engine mounting to the wing tip. To achieve laminar flow in the outer wing, nose suction panels are used and the wing shape is changed. The aerodynamic HLFC wing design is performed at different cruise flight conditions. It involves shape design and optimization of the suction distribution. The shape design was performed using the DLR 3D transonic inverse design code. Results for the shape design are presented for three geometries. The first one is a DLR redesign of an HLFC variant of the XRF1 aircraft designed by Airbus. This geometry is used for the HLFC-WIN ground base demonstrator. Design was performed at the cruise design point and for off-design conditions. This design presents two improvements in comparison to the initial geometry: a) an increased laminar extent for the cruise design point and b) an increased spanwise thickness distribution, which leads to a thickness distribution comparable to the reference geometry. A second HLFC design was performed which improved the cruise design point aerodynamic performance of the first design, also by reducing wave drag. In a third design it was shown that in the region of the outermost suction panel a natural laminar flow (NLF) design was possible by using for the nose a crossflow attenuated NLF (CATNLF) strategy. The shape design was performed on simplified geometries. For final shape designs complete configuration CFD solutions were obtained using the TAU RANS solver of DLR. The aerodynamic performance of the different HLFC geometries was assessed by using the ffd72 far-field drag analysis software of ONERA for these solutions. In the shape design a generalized suction distribution based on the suction distribution of the Airbus HLFC design was used. After the shape design, the suction distribution was optimized for the GBD-DLR-2 design in order to minimize the suction power. A novel combined approach of variable porosity outer skin and suction chambers was introduced. In addition to the design and analysis of the HLFC geometries this work also describes extensions of the numerical methods used to predict the transition line position in the case of boundary layer suction. The physical representation of surface suction was improved by implementing and testing a direct suction boundary in the TAU solver.