Numerical Simulation Of The Unsteady Aerodynamic Performance Of Vertical Wind Turbines

Vertical axis wind turbine gains more and more attention and develops to the large-scale gradually since it is applicable to any directions of wind without yaw device and its transmission device can be placed on the ground, it is convenient for operation and maintain. The manufacturing of the blade is also simpler comparing to horizontal axis wind turbines. And the cost and noise are also lower. The analysis and design of the wind turbine aerodynamic performance accurately to ensure the reliability and safety of the wind turbine are keystones of the rapid development of wind energy industry. The research method of the vertical axis wind turbine aerodynamic performance includes experimental method, model method and numerical method. The experimental method is difficult to implement and the measurement data is limited. The model method is the streamtube model based on Blade-element momentum theory. The numerical method includes the vortex model based on potential theory and the numerical simulation method based on Navier-Stokes equations. Neither the streamtube model nor the vortex model use the airfoil aerodynamic performance data getting from wind tunnel experiments to deal with the viscosity of the fluid. Currently, the CFD method plays a more and more important role in the study of the wind turbine aerodynamic performance with its outstanding advantages. Therefore, the CFD commercial software FlowVision HPC is used to study the unsteady viscous flow field in this paper. The SST turbulence model is used for turbulence modeling, which assumes the flow full turbulent.First of all, Two-dimensional unsteady viscous flow of H-type vertical axis wind turbine with one blade and three blades and three-dimensional unsteady viscous flow of H-type vertical axis wind turbine with three blades are numerically investigated by using a commericial CFD softeware FlowVision HPC. The calculated results are compared with the experimental data to determine the effectiveness of the calculation method. Variation of loads of single and three blades with azimuth is investigated. The unsteady flow details, the distribution of velocity and the motion of vortex shedding are analyzed. Three-dimensional numerical simulation calculation results are more close to the experimental value. The load of wind turbine is reduced by the unsteady vortex motion and dynamic stall phenomenon at low blade tip speed ratio. Installing the blade-tip plate on the top of the experimental model blade will reduce the strength of the tip vortex. The load of wind turbine will increased after pitch angles changed.Three-dimensional unsteady aerodynamic performance of H-type wind turbine with blade-tip plate which installed on the top of the experimental model blade is investigated with the same numerical simulation method in the condition of low, middle and high tip speed ratios. Variation of the relative velocity of blade tip and the pressure distribution of the blade suction are analyzed. The cause of the wind turbine aerodynamic load increased after installing blade-tip plate is revealed. Two-dimensional unsteady viscous flow of H-type vertical axial wind turbine with pitch angles changed is numerically investigated by using CFD numerical simulation method in this paper. The method of fixed pitch angles and pitch angles changging is used to change angles of attack. Power coefficients, aerodynamic load and the unsteady flow details through velocity and vorticy contours with azimuth in one rotation cycle are analyzed. The cause of the wind turbine aerodynamic load increased after pitch angles changed is revealed.The wake of the H-type wind turbine is complex and the unsteady flow of vortex shedding is also complex. The variation of the tangential force coefficient of single blade of upstream and downstream wind turbines with azimuth and the velocity distribution of different locations of the wind turbine wake are discussed in details with different distance between two experimental models. Two-dimensional unsteady viscous flow field through velocity, vorticity and turbulent kinetic energy contours in one circle is presented. Influence of the wake on aerodynamic performance of the downstream wind turbine is revealed in this paper, which provides reference for the layout of wind turbine in wind farm.The aerodynamic performance of a H-type vertical axis wind turbine which is an experiment model under self-starting is investigated. Based on the comparison between the computed time-dependent variations of the rotation speed with the experimental data, the time-dependent variations of the torque are presented. The characteristics of self-starting of the wind turbine are analyzed with different pitch angles. The influence of pitch angles variations on two-dimensional unsteady viscous flow field through velocity contours is discussed in detail.Finally, the method for calculating the aerodynamic performance of Φ-type wind turbine with uniform multiple streamtube and multiple streamtube models based on the momentum theory is proposed. In order to improve the accuracy of multiple streamtube models, additional resistance coefficient and dynamic stall modification are introduced into the implementation. Effect of the blade solidity and the height to diameter ratios on the aerodynamic performance is analyzed. The range of the solidity and the height to diameter ratios is suggested to design the wind turbine in the appendix of this paper.