Research On Flutter Tailoring Techniques Of High-Aspect-Ratio Wings

Aeroelasticity has always been considered as a high priority in aircraft design over the whole process of the aircraft development. The natural frequency of the first horizontal bending mode is low for the high-aspect-ratio wing. The horizontal bending mode interacting with the torsional mode yields flutter because of the geometric nonlinearity of the large displacement. And the consequence varies with the difference among the frequency of the horizontal bending mode, the vertical bending mode and the torsional mode. Therefore, it has its great engineering importance in the research of the nonlinear flutter character and to find the method to design.First of all, in this paper, a new method is presented to analysis the nonlinear flutter. Based on this method, the flutter characteristics of the high aspect wing are illustrated and the the feasibility of the design of nonlinear flutter is discussed. Based on these results, a simplified slender box section model is presented. And then the close mode on the influence law of nonlinear dynamics is implemented through the combination of different horizontal bending frequency and torsion frequency. The numerical results show that the flutter speed is decreased when the first horizontal bending mode involved. Thus, the increasing of the natural frequency of the first horizontal bending mode is helpful for improving the flutter speed. Moreover, the wing flutter speed descends significantly due to the coupling of the first horizontal bending mode and the torsion mode. The flutter pattern can be changed from the interacting of the first horizontal bending mode with vertical bending mode to the interacting of the first horizontal bending mode with the torsional mode.Secondly, this study discussed how the main direction of the composite influences the character of the nonlinear vibration and flutter, established the method of the flutter clipping to the high aspect wing. And the result shows that the stiffness of the structure can be changed by changing the main direction of the composite. It mainly changes the horizontal bending mode, makes the main direction tend to the Trailing edge, and then makes the section line moves to the leading edge. By further analyzing the nonlinear flutter, we discovered that it is the changing of the horizontal bending mode that causes the flutter speed changed obviously. And by the section line of this mode moves ahead, the flutter speed will become larger. In this study, we illustate two examples to validate its truthiness and we also discovered that the more behind the main stiffness is, the larger positive degree of the reverse is, and then the small static divergent speed is. In general, the design of the composite’s main direction is a process of integrated design, and there is a contradiction between the flutter and static divergence. For the purpose to get a satisfactory design, we have to take both the flutter and static divergence in to consideration.In the end, the study explored a method of the integrated aeroelasticity optimization in the preliminary design process. This method contained nonlinear flutter, nonlinear static divergence, and static strength, considered the influence of layer’s thickness, direction, and the structure arrangement to the aeroelasticity. And also, it made a combination of the test design to the approximation technique like quadratic response surface model and artificial neural network. And then established an approximation model of the flutter character and structure character, and made an optimization by using this. We use a model to implement the optimization of a composite high-aspect-wing’s nonlinear aeroelasticity, to explain the feasibility and the validity of this method.