The trend of large-scaling in wind turbines decreases the blade stiffness and lifts the risk of blade flutter. Meanwhile, the blade is also inevitably affected by the non-uniform inflow during real-world operations. To inquire into this problem, the aeroelastic stability of airfoil with structural nonlinearities placed in vertically fluctuating non-uniform inflow is investigated. Based on the assumption of small angle of attack, taking the cubic-stiffening suspension and non-uniform inflow into account,a two-dimensional,two-degrees-of-freedom aeroelastic model is established by using the linear aerodynamic modle. The dynamic equation of the aeroelastic systern for airfoil is then solved via numerical integration method, and the steady-state response forms of air foil system under different inflow conditions are obtained. The characteristics of the oscillation signal are analyzed from the time-, phase- and frequency- domains. The results show that the airfoil undergoes forced oscillation caused by the excitation of the vertical inflow. The non-uniform inflow also amplifies the flutter at low and near-critical airspeeds, obscures the boundary of the flutter onset, and makes the induced flutter conditions of the airfoil more severe. It is also found that the pitch oscillations have a frequency distribution which peaks at higher than the flutter frequency,indicating that the flutter onset is caused by the frequency shift from the pitch to the plunge oscillations.
Key words
wind turbines /
aeroelasticity /
flutter /
numerical analysis /
structural nonlinearity /
non-uniform inflow
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References
[1] LEE B H K, PRICE S J, WONG Y S. Nonlinear aeroelastic analysis of airfoils: bifurcation and chaos[J]. Progress in aerospace sciences, 1999, 35(3): 205-334.
[2] ABDELKEFI A, VASCONCELLOS R, NAYFEH A H, et al.An analytical and experimental investigation into limit-cycle oscillations of an aeroelastic system[J]. Nonlinear dynamics, 2013, 71(1-2): 159-173.
[3] LEE Y S, VAKAKIS A F, BERGMAN L A, et al.Triggering mechanisms of limit cycle oscillations due to aeroelastic instability[J]. Journal of fluids and structures, 2005, 21(5): 485-529.
[4] GAO Q, CAI X, GUO X W, et al.Parameter sensitivities analysis for classical flutter speed of a horizontal axis wind turbine blade[J]. Journal of Central South University, 2018, 25(7): 1746-1754.
[5] IRANI S, AMOOZGAR M, SARRAFZADEH H.Effect of sweep angle on bifurcation analysis of a wing containing cubic nonlinearity[J]. Advances in aircraft and spacecraft science, 2016, 3(4): 447-470.
[6] ROBINSON B, DA COSTA L, POIREL D, et al.Aeroelastic oscillations of a pitching flexible wing with structural geometric nonlinearities: theory and numerical simulation[J]. Journal of sound and vibration, 2020, 484: 115389.
[7] VAN ROOIJ A C L M, NITZSCHE J, DWIGHT R P. Energy budget analysis of aeroelastic limit-cycle oscillations[J]. Journal of fluids and structures, 2017, 69: 174-186.
[8] RAAJ A, VENKATRAMANI J, MONDAL S.Synchronization of pitch and plunge motions during intermittency route to aeroelastic flutter[J]. Chaos: an interdisciplinary journal of nonlinear science, 2019, 29(4): 43129.
[9] VENKATRAMANI J, KUMAR S K, SARKAR S, et al.Physical mechanism of intermittency route to aeroelastic flutter[J]. Journal of fluids and structures, 2017, 75: 9-26.
[10] VENKATRAMANI J, NAIR V, SUJITH R I, et al.Precursors to flutter instability by an intermittency route: a model free approach[J]. Journal of fluids and structures, 2016, 61: 376-391.
[11] 朱呈勇, 王同光. 振荡翼型和振荡来流下的动态失速数值研究[J]. 太阳能学报, 2019, 40(9): 2433-2440.
ZHU C Y, WANG T G.Numerical investigation into dynamic stall under pitch oscillation and oscillating freestream[J]. Acta energiae solaris sinica, 2019, 40(9): 2433-2440.
[12] DOS SANTOS L G P, MARQUES F D. Nonlinear aeroelastic analysis of airfoil section under stall flutter oscillations and gust loads[J]. Journal of fluids and structures, 2021, 102: 103250.
[13] FUNG Y C.An introduction to the theory of aeroelasticity[M]. New York: John Wiley, 1955.
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