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Numerical Analysis of Vortex-induced Vibration of the Wind Turbine Airfoil under Big Angle of Attack

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Tutor: WangJun
School: Huazhong University of Science and Technology
Course: Fluid Machinery and Engineering
Keywords: Double wake model,Wind turbine airfoil,Numerical simulation,Lock-in phenomenon,V
CLC: TM315
Type: Master's thesis
Year:  2013
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As the size of the wind turbine is becoming larger and larger, the flow inducedvibration problem of the parked wind turbine is being increasingly concerned. In this study,the vortex-induced vibration of the wind turbine blade airfoil cross-section is investigatedthrough numerical simulation. The simulation model employed in this study is a doublewake model based on the vortex-type panel method of the potential flow theory. Thepresent study mainly includes the following4parts:(1). The parametric study of the numerical code. The main goal of this part is to knowhow the model parameters influence the simulation result, and to find appropriatevalues for the following simulations.(2). The steady aerodynamic performance prediction of the highly stall part with theangle of attack varying from60ˇăto120ˇă. Of the prediction results, the bestsimulated Clcurve meets the experimental one perfectly, and the Cdcurve has onlyabout10%discrepancy with the experiments. Through FFT analysis of the Cltimeseries, the Strouhal number obtained is equal to0.1under the angle of attack90ˇă.(3). During this part, a chord-wise sinusoidal vibration is imposed on the airfoil. Bychanging the vibrating amplitude and frequency, the lock-in phenomenon of theairfoil under90ˇăis studied. The results show that the energy fed into the airfoilincreases as the airfoil vibration frequency getting close to the vortex sheddingfrequency. At the same time, the coupling between the Cland x indicates theemergence of lock-in phenomenon. With the increase of vibration amplitude, thelock-in is strengthened and the lock-in area is broadened further. What is more, it isfound that there is a positive feedback between the lock-in and airfoil vibration,which is probably one of important reasons for the occurrence of vortex-inducedvibration.(4). An elastic model with3degrees of freedom is coupled with the double wake modelto simulate the free vibration response of the elastically mounted airfoil. Withoutconsidering the structural damping, it shows that the edgewise airfoil vibrationdiverges when the edgewise natural frequency is equal to the vortex shedding frequency, which means the resonance induced by vortex shedding occurs under thiscondition. As the natural frequency moves away from the vortex shedding frequency,the vibration strength decreases. After that, with the consideration of structuraldamping, it is found that the larger damping ratio, the weaker the vibration response.In all, the aerodynamic performance of a wind turbine airfoil in high stall region ispredicted with the double wake model. The lock-in phenomenon is obtained and themechanism of vortex-induced vibration is analyzed in the prescribed motion simulation.The vibration response of the elastically mounted airfoil and the effect of structuraldamping on the response are studied by coupling a structural model with the double wakemodel.
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