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Considering the drag-divergence performance as a constraint, this paper presents a multi-point aero-structural design optimization of wings on a wing-body-tail-engine configuration of long-range dual-aisle civil aircraft by using a gradient-based method based on the discrete adjoint method. Firstly, the accuracy of the coupled aero-structural analysis method used in this paper was validated with DLR-F6 wing-body configuration. Then a wing aero-structural design optimization based on a dual-aisle civil aircraft is offered. The drag coefficient of the optimized configuration in every state decreased, which was reduced by 13.67 counts at the cruise condition, the difference in drag coefficient from Mach 0.85 to Mach 0.87 was decreased from 28.52 counts to 18.98 counts, indicating its drag-divergence performance has been improved undoubtedly. Finally, we compared the performance among the multi-point aero-structural optimized configuration, the single-point aerodynamic optimized configuration and the single-point structural optimized configuration. The results show that the multi-point aero-structural design optimization considering drag-divergence performance has great potential to gain a design configuration with better comprehensive and practical performance compared with a single-point optimization in a single discipline.

This paper studies several problems that may exist in the aerodynamic design of low Mach number general aircraft, and discusses the design characteristics of the pressure distribution of some related airfoils while part of the characteristics is verified by a multi-point laminar airfoil design case. Firstly, several issues which exist in the aerodynamic design of low Mach number general aircraft, such as relatively large zero-lift drag coefficient, high stall performance requirements, and large variation range of Reynolds number, are discussed and analyzed. Then, to address these issues, the paper extracts some useful design features that are beneficial to the airfoil aerodynamic performance from the study on the design characteristics of the pressure distribution of several turbulent flow airfoils and laminar flow airfoils that are designed for low Mach number general aircraft. Finally, by considering the typical design conditions of a light multi-purpose single-turboprop-engine general aircraft, including the cruise, climb and stall conditions, a multi-point laminar airfoil optimization is offered by using the GAW-1 airfoil as the baseline. The optimized foil has a 9.6 improvement in the lift-to-drag ratio of the cruise condition, a 16.3 improvement in the lift-to-drag ratio of the climb condition but a 0.115 decrease in the maximum lift coefficient of the stall condition. The results show that the requirements from the cruise, climb and stall conditions are contradictory to some degree in the considering multi-point optimization case, and the designers should deal with this trade-off carefully based on the features of the low Mach number general aircraft.

The aerodynamic noise of a landing gear is an important source of airframe noise. The analysis of its noise characteristics plays an important role in the design of a low-noise landing gear. Based on the FL-52 acoustic wind tunnel test technology, the coupled scale adaptive model and the acoustic disturbance equation, the results on aerodynamic noise of a full-scale landing gear model are analyzed. The high-fidelity model includes transverse strut, torsion arm, piston rod, wheel and other parts. The characteristics of static pressure distribution, power spectrum density of pulsating pressure, aerodynamic noise source distribution and directivity of overall sound pressure level are analyzed. The noise characteristics of the far-field microphone are compared with the local microphone installed in the wheel cavity. In this way, we characterize the directivity of pure tone in the wheel cavity and understand its contribution to the far-field noise. The results show that the aerodynamic noise of the landing gear can be quantified accurately by the hybrid numerical method. The pure tone has two frequencies inside and outside the wheel of the landing gear: 560 Hz and 960 Hz. The peak of the loudest sound pressure level reaches 136 dB, and the pure tone radiates to the surface of the non-separation area of the wheel of the landing gear. However, the wall pressure spectrum of the points located in the turbulence region shows a wide-frequency characteristic, and there is no obvious pure tone. From the point of view of the far-field noise directivity, the forward noise of the landing gear is larger than the rear noise, and there is a small overall sound pressure level area at the points of 65 and 110 degrees respectively. When the monitoring points are far away, the far-field noise of the landing gear shows the characteristics of wide frequency, and no obvious pure tone appears. The method can provide the technical support for predicting the aeroacoustics of a landing gear and designing a low-noise land gear.