The Aeroelastic Characteristics Analysis Of The High-Aspect-Ratio Wing

Under the effects of aerodynamics, elastomer will vibrate and deform, which in return cause the redistribution of the original aerodynamics. Then the aeroelastic problems come with the coupling effect of the aerodynamic and the elastic force. Actually, aircrafts that fly in the moving airflow can never avoid the aeroelastic problems. That is why more and more attentions are paid to the aircraft aeroelastic problems in engineering designs. During the past two decades, large passenger aircrafts and UAVs(Unmanned Aerial Vehicles), which have high-aspect-ratio, light structure weight and great flexibility, come across the flutter problems more frequently due to their requirements of higher height and longer flight time. So the aeroelastic analysis of high-aspect-ratio and more flexible wings is extremely urgent. And how to find out a low-cost method which is able to reflect the effects of a wing’s small strain and large deformation has become a difficult problem.This essay will focus on the high-aspect-ratio flexible wings, doing researches on geometric nonlinear effects throughout the flight. The “Quasi-Mode” method is chosen for aeroelastic analysis on wings. We dig deep, add the actual static aeroelastic preloads to the wing structure, and do the flutter analysis on high-aspect-ratio wings. This report contains the following contents:1. Based on the analysis on system structural dynamic changes under the Goland wing preload, we find that the Goland wing will buckling as the loads on the wing tip increase. And the first two order inherent frequencies get closer according to the geometric nonlinear quasi mode method. If we apply the Frequency Superposition Theory to this phenomenon, the conclusion is that under an actual large deformation situation, i.e. geometric nonlinear situation, the Goland wing will have a smaller flutter velocity than that worked out by a traditional mode analysis method. That is to say, form the angle of structural dynamics, the traditional flutter analysis on wings is not conservative enough, since it may lead to a flutter danger in practice when dealing with the high-aspect-ratio wings.2. Analyze the static aeroelasticity of a Goland wing, work out the actual aerodynamic loads on the Goland wing during a flight by DLM, and add the loads on the Goland wing for structural dynamic analysis. It turns out that the first three order inherent frequencies get closer as both the angle of attack and the aerodynamics go larger. The flutter theory proves that the flutter velocity of high-aspect-ratio wings under the quasi mode method will be slower than that based on the small strain assumption, which emphasizes the necessity of taking the geometric nonlinear effects into consideration when doing flutter analysis for high-aspect-ratio wings. Besides, it tells that as the angle of attack and the lift increase, the geometric nonlinear effects of a Goland wing become more obvious and the flutter velocity decreases.3. Using the g method to solve for the flutter velocity of a Goland wing based on the small strain assumption, we have studied the computing methods about this kind of wing flutter and figured out a flutter form for it. And this will serve as the contrast example to our result from the “Quasi Mode” method. The Goland wing’s flutter velocities under different aerodynamic conditions are calculated to draw a flutter velocity curve and an aerodynamic(velocity) curve. Through the condition that the abscissa equals the ordinate, we can obtain the flutter velocity for a certain angle of attack. Following this line, the variation law of flutter velocities when the structural dynamic changes under aerodynamics are considered is found. What’s more, we reach a conclusion that the bigger the angle of attack, the smaller the flutter velocity.