Analysis And Application Of Aerodynamic Damping

Wind turbine blades which are in normal operation or parking often vibrate severely and damage when wind speed is far below the design extreme wind speed. The relatively accurate aerodynamic damping model and structure vibration model of wind turbine blade are created, and the model of the dynamic loads calculation for the horizontal axis wind turbine (HAWT) are combined in this paper to realize aerodynamic damping model and structure reaction of the HAWT. With the tool of Visual C++, the aerodynamic damping and structure reaction modules of the blade are developed. The paper consists of three parts: aerodynamic analysis and calculation theory, aerodynamic damping model, and structure reaction model of the blade.The aerodynamic analysis and calculation section first discusses the traditional analysis and calculation theory. Based on the traditional theory the aerodynamic analysis and dynamic load calculation model is developed. The dynamic load calculation model calculates the wind velocity with time series and aerodynamic force coefficient of airfoil with turbulent wind field model and dynamic stall model. It breaks the restriction of the traditional theory which only supports stationary calculation.Aerodynamic damping is based on the calculation of aerodynamic loads and structural reaction theories of the blade. It can acquire that aerodynamic damping is heavily dependent on CL,CD and their changing ratios with angle of attack, structure parameters of wind turbine blades and external wind conditions. When the aerodynamic damping is negative it can provide energy for the vibration of the blade which can explain the problem of the damage of blade. By constructing the relationship among aerodynamic damping, power and thrust force, it can be concluded that power and thrust force have important influence on aerodynamic damping. Aerodynamic damping model provides the basis for the reliability and optimum design of wind turbine blade and wind turbine control methods.Structure reaction model of the blade is based on blade mode shapes and after calculating the frequencies under modes through Ritz method, then combing calculated aerodynamic damping and the models of free vibration and forced vibration, the structure vibration model of the blade is got finally. By adding resonance force to make blade resonance vibration, it can be concluded from the response of the blade vibration the aerodynamic damping provides energy for blade vibration which results in divergent vibration of the blade when the aerodynamic damping is negative. The aerodynamic load and aerodynamic damping can be accurately calculated by applying this model. It is also useful for researching on the gas-structure coupling.