A Study of Transport Aircraft High-Lift Design Approaches

Abstract

The high-lift design process is focused in obtaining the best aerodynamic shape and the optimized position for the high-lift devices. The main requirement for the design process is strongly connected with the need to achieve a maximum target lift coefficient for the landing and take-off maneuvers. In this context, the present work has the objective of presenting two numerical methodologies to predict the maximum lift coefficient, namely, the quasi-3D and the 3D approaches. The NLR7301 airfoil configuration has been chosen for the study, since it is a non-proprietary geometry. The numerical simulations are performed with the CFD++ and VSAERO commercial codes. The meshes are created with the ICEM mesh generator. The work also presents a sensitivity analysis of the aerodynamic parameters, such as the global 3-D lift coefficient or the section lift coefficient, with regard to changes in the numerical setup. In the present study, the results obtained by the two methodologies showed a certain level of discrepancy. A dispersion of about 6% in the prediction of the maximum C L was obtained by the quasi-3D analysis, while the 3D methodology presented a premature stall. I. Introduction he high-lift design process is focused in obtaining the best aerodynamic shape and the optimized position for the high-lift devices. The main requirement for the design process is strongly connected with the need to achieve a maximum target lift coefficient (C L) for the landing and take-off maneuvers. The definition of the target landing/take-off maximum C L depends on the mission to be carried out by the airplane. The design process must be effective in achieving the target C L due to the penalization that a bad design can cause on some macro variables related with the performance or the operation of the airplane. The subject of high-lift devices has always been an area of special interest to airplane designers. The accurate prediction of pressure distributions, boundary layer confluences, and detached flow regions over the multi-element high-lift wings plays a fundamental role in the design of high-lift devices. The complex physical phenomena involved in such flowfield are responsible for the difficulty associated with high-lift design. It is important to observe that currently most of the aerodynamic design is performed with the aid of CFD. Lately, the advance of CFD has produced an important change in the form in which aerodynamic analysis and design are performed in the aeronautical industry. CFD has reached such a level of importance that one cannot imagine an aerodynamic department without a CFD group. The constant development of CFD, as a tool capable of producing complex analyses, has been responsible for the spread of its use all over the world. Until a few years ago, aerodynamic design was driven by simplified analytical methods and empirical formulations, together with massive wind tunnel campaigns to validate the aerodynamic design. Today the fierce competition between the aeronautical manufacturing companies does not allow such a costly design procedure anymore. The current tendency encourages the use of wind tunnel tests just as a way to corroborate the aerodynamic design, previously performed with CFD. 1-2 The world aeronautical manufacturing companies are eager to reduce the inherently high cost associated with wind tunnel tests. In order to give an idea of the amount of money required for a wind tunnel campaign, the milled model costs might reach the order of hundreds of thousands of dollars. This cost intrinsically depends on whether the model is a full or a half model, and its geometric complexity. The cost of the test might start at a few hundreds of thousands of dollars and reach the mark of millions