Analysis Of Added Damping And Flutter Of High Aspect-ratio Wing Based On ARMA Model

In recent years,with the development of major national projects such as high-altitude long-endurance drones,solar-powered aircraft,and large wind turbines,the thin airfoil structure of these major project equipment can improve aircraft endurance,flight capability,and fan efficiency.And It has a decisive influence on preventing equipment destructive vibration or fatigue failure.Previous studies have shown that the thinner the airfoil and the larger the aspect ratio,the more conducive to saving materials and improving its performance,but it will also cause more complex nonlinear deformations,which in turn will cause more complex fluid-structure interactions.At present,there are relatively few studies on the fluid-structure interaction of such thin airfoil with large aspect ratio,and the existing research mainly focuses on numerical simulation,with relatively few experimental research data,and experimental research data is not comprehensive enough.In this paper,the NACA0012 airfoil is used to design the wing,the aspect ratio of the wing is 9,and the flexible beam is used as the support,and the two ends of the wing are fixed.Based on wind tunnel experiments,the added damping and flow field characteristics of the wing at an angle of attack of 0°to 90°are studied.Compared with other articles,this article can describe the flutter deformation and flow field characteristics of the large aspect ratio flexible wing more comprehensively and in detail.And this article uses the time series ARMA model method to explain the flutter mechanism of the wing in the experiment by analyzing the damping changes.It can provide some explanations for the fluid-structure coupling effect flutter phenomenon that may occur in the practical application and improve ideas to prevent flutter.Based on time-domain autoregressive moving average(ARMA)iterative model,this article studied the added damping changes of a large aspect ratio flexible wing at the angle of attack of 0 to 90 degree.Firstly,the correctness of the ARMA program is verified through simulation and experimental data.The ARMA method is used to analyze the added damping changes of the vortex-induced vibration of the cylinder in the fluid.The study shows that as the reduction speed U_r increases,the total damping will decrease and the total damping will be 0 at resonance.The amplitude and damping will be inversely proportional.The analysis results are consistent with the results of previous articles.Furthermore,the ARMA method is used to analyze the added damping changes of the wing in the flow field.The study found that the bending added damping of the wing gradually decreases with the increase of the angle of attack,the fluid produces a positive added damping,and the amplitude is inversely proportional to the damping.In this paper,the deformation and flow field characteristics of the large aspect ratio flexible wing are studied in detail and comprehensively during fluttering,and its damping mechanism is introduced.At 0.5 degree angle of attack,the flutter is classical flutter.The fluid is always attached to the surface of the wing,and the bending deformation is larger.The bending frequency is coupled with the torsion frequency,and the total torsion damping is 0,which causes flutter.At 2～8 degree angle of attack,the flutter is stall flutter.There are periodic flow separation and vortex separation,and the torsional deformation gradually increases.Periodic flow separation and vortex shedding are consistent with the torsion natural frequency,which leads to resonance,and the total torsion damping drops to 0,which causes flutter.