Aerodynamic Optimization Of Civil Aircraft Design Based On Advanced Computational Fluid Dynamics

Wing is the most important component of a civil aircraft. Its aerodynamic characteristics have direct effect on fuel consumption, emission, safety and comfortability of the civil aircraft. In order to ensure the future China homemade civil jet successful in the market, innovation in design technology and theory is vital. In the present thesis, an optimization system based on the advanced CFD method is developed along with the design practice of the China civil jet. Design theory is summarized for the wing design. The key flow phenomena are studied. Engineering applicable designs of supercritical wing, wing nacelle integration and multi-element airfoil have been successfully achieved.Four conflicts in the current methodology of design optimization are considered as the main problems for engineering applicability. They are the conflicts between speed and accuracy, human experience and automatization of optimization, component design and full configuration design, local vs. global optimization methods. An optimization system is formulated by solving these four conflicts. Mathematical definition of constraints for supercritical pressure distribution and NURBS increment curve for modification of airfoil are developed for supercritical wing design. Personal experience and automatic optimization are well combined in the design process.High-order conservative remapping method is developed to improve the CFD analysis code NSAWET's window embedment technique. The accuracy of flow field information exchange on non-matched grid interface is improved. Several standard test cases are used for comprehensive verification of the NSAWET code.Aerodynamic characteristics of three typical pressure distributions of supercritical wing are systematically studied. For the present civil jet, the pressure distribution with a weak shock wave could archieve good cruise efficiency and robustness. The location of the shock is found better to move somewhat upstream than that of the normal supercritical airfoils. Supercritical wing of the China civil jet is optimized by using RANS simulation along with genetic algorithm. The results show that, multi-point optimization is a good approach to improve the engineering applicability of the wing design. A dual-point optimization is conducted to minimize the drag at both the cruise and the drag divergence Mach numbers. The results of wind tunnel test match well with the present design, and verified the performance of the design.Wing/nacelle integration design is also completed for the China civil jet. The influence of nacelle installation is numerical investigated. Wing geometry is optimized with the influence of nacelle installation. Results show that the nacelle decreases the local angle of attack to the middle part of the wing. Results of the single point optimization show that the drag reduction from the potential of the shock-free design is very small (about 1 drag count) and the off-design characteristic is not acceptable in practice. A weak shock design is finally realized from the dual-point optimization. The final wing nacelle integrated design is achieved through artificial modification on the dual-point design to improve the low-speed stall behavior and buffet characteristics. The final design is shown to exhibit significantly better performances than the similar civil aircrafts of the similar type in the market.The influence of the installation and shape parameters of the multi-element airfoil is numerical investigated. Slope of lift curve's non-linear up-turn near the stall angle is studied. Competition between the jet from the gap and the trailing edge vortex on the flap is believed to be the cause. Multi-point optimization is successfully applied to eliminate the non-linearity of the lift curve.